Positive electrode material and preparation method therefor, sodium secondary battery, and electric device

Abstract

The present application relates to the technical field of batteries, and specifically to a positive electrode material and a preparation method therefor, a sodium secondary battery, and an electric device. The positive electrode material comprises single-crystal particles and / or quasi-single-crystal particles of a layered transition metal oxide. The design method provided by the present application is conducive to prolonging the cycle service life of the sodium secondary battery.

Description

Cathode material, preparation method thereof, sodium secondary battery and electric device

[0001] Cross-reference to related applications

[0002] This application claims priority to Chinese Patent Application No. 202411244945.8, filed on September 5, 2024, entitled “Cathode material, preparation method thereof, sodium secondary battery and electric device”, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0003] The present application relates to the field of batteries, in particular to a cathode material, a preparation method thereof, a sodium secondary battery and an electric device. BACKGROUND

[0004] Secondary batteries are widely used in various consumer electronic products and electric vehicles due to their light weight, no pollution, no memory effect and other outstanding characteristics.

[0005] With the increasingly wide range of applications of secondary batteries, the requirements for battery performance are also becoming higher and higher. SUMMARY

[0006] In view of the above problems, the present application provides a cathode material, a preparation method thereof, a sodium secondary battery and an electric device, which improve the cycle service life of the sodium secondary battery by increasing the content of single crystal particles and / or quasi-single crystal particles in the cathode material.

[0007] In a first aspect, the present application provides a sodium secondary battery, which comprises a cathode sheet, a separator and an anode sheet arranged in layers; the cathode sheet comprises a cathode current collector and a cathode film layer located on at least one side surface of the cathode current collector; the cathode film layer comprises a cathode active material; the cathode active material comprises single crystal particles and / or quasi-single crystal particles of layered transition metal oxides; the shape of the single crystal particles and / or quasi-single crystal particles comprises any one or more of spherical, quasi-spherical, polygonal sheet-shaped and polygonal columnar;

[0008] and the cathode active material satisfies the following conditions:

[0009] (1) the volume particle size distribution Dv50 is 3 μm to 7 μm;

[0010] (2) the specific surface area BET is 0.3 m 2 / g to 0.5 m 2 / g.

[0011] In some embodiments of the present application, the mass percentage content of the single crystal particles in the above-mentioned cathode active material is 20% to 40%.

[0012] In some embodiments of the present application, the mass percentage content of the quasi-single crystal particles in the positive electrode active material described above is 60% to 80%.

[0013] In some embodiments of the present application, the volume particle size distribution Dv50 of the single crystal particles is 5 μm to 7 μm.

[0014] In some embodiments of the present application, the volume particle size distribution Dv50 of the quasi-single crystal particles is 3 μm to 5 μm and does not include 5 μm.

[0015] In some embodiments of the present application, the chemical formula of the layered transition metal oxide is Na x M y O z , wherein M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, 0

[0016] In some embodiments of the present application, the layered transition metal oxide is a nickel-iron-manganese-based layered transition metal oxide, and the chemical formula of the nickel-iron-manganese-based layered transition metal oxide described above is NaNi a Fe b Mn c M1 d O2, wherein a+b+c+d = 1, 0≤a≤1, 0≤b≤1, 0≤c≤1, 0≤d≤1, and M1 is selected from one or more of Co, Cr, V, Al, Sn, B, Cu, Fe, Li, Ti, Mg or Zn.

[0017] In some embodiments of the present application, the compaction density of the positive electrode film layer is 3.0 g / cm 3 ~ 3.4 g / cm 3 .

[0018] In some embodiments of the present application, the sodium secondary battery further comprises an electrolyte, and the electrolyte comprises any one or more of a carboxylic acid ester compound, a carbonate compound, and an ether compound.

[0019] A second aspect of the present application is to disclose a positive electrode active material for a sodium secondary battery, the positive electrode active material comprising single crystal particles and / or quasi-single crystal particles of a layered transition metal oxide;

[0020] The shape of the single crystal particles and / or quasi-single crystal particles described above comprises any one or more of a spherical shape, a quasi-spherical shape, a polygonal flake shape, and a polygonal columnar shape.

[0021] The positive electrode active material described above satisfies the following conditions:

[0022] (1) The volume particle size distribution Dv50 is 3 μm to 7 μm;

[0023] (2) the specific surface area BET is 0.3 m 2 / g ~ 0.5 m 2 / g.

[0024] In some embodiments of the present application, the mass percentage content of the single crystal particles in the above-mentioned positive electrode active material is 20% ~ 40%.

[0025] In some embodiments of the present application, the mass percentage content of the single crystal particles in the above-mentioned positive electrode active material is 20% ~ 40%.

[0026] In some embodiments of the present application, the volume particle size distribution Dv50 of the single crystal particles is 5 μm ~ 7 μm.

[0027] In some embodiments of the present application, the volume particle size distribution Dv50 of the single crystal particles is 5 μm ~ 7 μm.

[0028] In some embodiments of the present application, the tap density of the positive electrode active material is 1.55 g / cm 3 ~ 1.80 g / cm 3 .

[0029] The third aspect of the present application is to provide a preparation method of a positive electrode active material for a sodium secondary battery, the preparation method comprising:

[0030] providing a positive electrode material precursor;

[0031] preparing a positive electrode material intermediate product: taking the positive electrode material precursor and mixing with sodium carbonate, and performing first calcination to obtain the positive electrode material intermediate product, wherein the positive electrode material intermediate product contains polycrystal particles of layered transition metal oxide;

[0032] preparing a positive electrode active material: taking a dispersant and dispersing into a solvent to form a mixed solvent, and dispersing the above-mentioned positive electrode material intermediate product into the above-mentioned mixed solvent, and performing second calcination to obtain the positive electrode active material, wherein the positive electrode active material contains single crystal particles and / or quasi-single crystal particles of layered transition metal oxide, and the mass percentage content of the single crystal particles and the quasi-single crystal particles in the above-mentioned positive electrode active material is > 98%;

[0033] The above-mentioned dispersant satisfies the following conditions:

[0034] (1) the dispersant is soluble in one or more of alcohol solvents, acetone, and water;

[0035] (2) the decomposition temperature of the dispersant is less than or equal to 600 ℃, and the decomposition temperature of the dispersant is the temperature corresponding to the decomposition peak of the thermogravimetric curve of the dispersant.

[0036] In some embodiments of the present application, the dispersant includes polyvinylpyrrolidone and modified compounds thereof.

[0037] In some embodiments of the present application, the dispersant is added in an amount of 0.5% to 5% by mass of the solvent.

[0038] In some embodiments of the present application, the volume ratio of the intermediate product of the positive electrode material to the mixed solvent is (10g to 20g) to (20mL to 100mL).

[0039] In some embodiments of the present application, the solvent includes one or more of an alcohol solvent, acetone, and water.

[0040] In some embodiments of the present application, the alcohol solvent includes one or more of ethanol, ethylene glycol, and glycerol.

[0041] In some embodiments of the present application, the first calcination temperature is 850°C to 970°C, and the holding time is 7h to 15h.

[0042] In some embodiments of the present application, the second calcination temperature is 600°C to 1000°C, and the holding time is 3h to 24h.

[0043] In some embodiments of the present application, the first calcination and the second calcination are performed in an oxygen-containing atmosphere.

[0044] In some embodiments of the present application, after the intermediate product of the positive electrode material is dispersed in the mixed solvent and before the second calcination, the method further includes:

[0045] The mixed solvent is heated and stirred until the solvent is evaporated.

[0046] In some embodiments of the present application, after the first calcination, the method further includes coarse crushing, fine crushing, and sieving to obtain the intermediate product of the positive electrode material, wherein the volume particle size distribution Dv50 of the intermediate product of the positive electrode material is 8μm to 12μm.

[0047] In some embodiments of the present application, the molar amount of the metal atoms in the positive electrode material precursor is N1, and the molar amount of the sodium atoms in the sodium carbonate is N2, and N1 / N2 satisfies 1:(0.5 to 1.1).

[0048] A fourth aspect of the present application is to provide an electric device, which includes the sodium secondary battery of the first aspect or the positive electrode active material of the second aspect or the positive electrode active material prepared by the preparation method of the third aspect.

[0049] The above description is only a summary of the technical solutions of the present application. In order to enable one skilled in the art to better understand the technical means of the present application and to implement the same according to the contents of the description, and in order to enable the above and other purposes, characteristics and advantages of the present application to be more apparent and easy to understand, the following specific embodiments of the present application are described. BRIEF DESCRIPTION OF DRAWINGS

[0050] Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The accompanying drawings are included to provide a description of the preferred embodiments and are not meant to limit the present application. Moreover, the same reference numerals in the drawings indicate the same or similar elements. In the drawings:

[0051] FIG. 1 is a schematic diagram of a battery structure according to some embodiments of the present application;

[0052] FIG. 2 is a schematic diagram of an exploded structure of a battery according to some embodiments of the present application;

[0053] FIG. 3 is a schematic diagram of a vehicle structure according to some embodiments of the present application;

[0054] FIG. 4 is a schematic diagram of a battery pack structure according to some embodiments of the present application;

[0055] FIG. 5 is a schematic diagram of a sodium secondary battery structure according to some embodiments of the present application;

[0056] FIGS. 6A and 6B are schematic diagrams of a positive electrode sheet structure according to some embodiments of the present application;

[0057] FIGS. 7A, 7B, 8A, 8B, 9, 10, 11A, 11B, and 12 are scanning electron microscope images of positive electrode materials prepared in some preparation examples and comparative examples of the present application.

[0058] The reference numerals in the detailed description are as follows: 10000, vehicle; 1000, battery; 2000, controller; 3000, motor; 100, battery cell; 200, case; 210, first part; 220, second part; 10, secondary battery; 101, housing; 102, electrode assembly; 103, cover plate; 1, negative electrode sheet; 2, positive electrode sheet; 21, positive electrode current collector; 22, positive electrode film layer; 3, separator; first direction: coordinate axis x direction, which can also be the stacking direction or the separator thickness direction; coordinate axis y direction: separator length or width direction. DETAILED DESCRIPTION

[0059] Hereinafter, specific embodiments of the positive electrode material, the method for manufacturing the same, the sodium secondary battery, and the electric device according to the present application will be described in detail with appropriate reference to the accompanying drawings. However, there will be cases where unnecessary detailed description is omitted. For example, there will be cases where detailed description of matters known to those skilled in the art, repeated description of substantially identical configurations, is omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0060] The ranges disclosed herein are defined by their lower and upper limits. Ranges can be defined by a lower limit and an upper limit, and the lower and upper limits define the boundaries of the particular range. Ranges can be inclusive or exclusive of the end values, and can be arbitrarily combined, i.e., any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed, it is understood that ranges of 60-110 and 80-120 are also contemplated. Furthermore, if a minimum range value of 1 and 2 is listed, and if a maximum range value of 3, 4, and 5 is listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present application, unless otherwise stated, a numerical range "a-b" indicates a shorthand way of describing each and every integer between the number "a" and the number "b", wherein "a" and "b" are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0" and "5" have been listed herein, and "0-5" is merely a shorthand way of describing those numerical combinations. Additionally, when a parameter is stated to be an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and the like.

[0061] If not specifically stated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0062] If not specifically stated, all technical features and optional technical features of the present application can be combined with each other to form new technical solutions.

[0063] If not particularly specified, all steps of the present application can be performed in sequence or randomly, preferably in sequence. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method can further comprise step (c), which means that step (c) can be added to the method in any sequence, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0064] If not particularly specified, the terms "comprise" and "contain" mentioned in the present application mean open type, and can also mean closed type. For example, the terms "comprise" and "contain" can mean that other components not listed can also be included or contained, or can mean that only the listed components are included or contained.

[0065] If not particularly specified, in the present application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any one of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or A and B are both true (or exist).

[0066] If not particularly specified, in the present application, the terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0067] If not particularly specified, in the present application, the term "a plurality of" means more than two (including two), and similarly, "a plurality of groups" means more than two groups (including two groups), and "a plurality of pieces" means more than two pieces (including two pieces).

[0068] If not particularly specified, the technical terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only used for the convenience of describing the embodiments of the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements indicated must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the embodiments of the present application.

[0069] Secondary batteries have been widely used in various products due to their high energy density, long cycle life, safety and reliability, etc. In recent years, with the significant increase in demand for secondary batteries as energy sources, higher requirements have been placed on the performance of secondary batteries, such as cycle life.

[0070] Sodium secondary batteries are expected to become one of the new low-cost energy storage technologies due to their cost and resource advantages and similar working principles to lithium batteries. The core technology of sodium secondary batteries lies in electrode materials. According to the micro-morphology of electrode materials, the positive electrode materials of sodium secondary batteries can be divided into single crystals and polycrystals. Single-crystal anodes have higher load voltage, which can improve the energy density. Moreover, single-crystal materials have no grain boundaries, and higher crystallinity, layered stability and anisotropy performance make them have better safety and cycle performance. In addition, single crystals have smaller surface area, which can reduce the occurrence of interface side reactions to a certain extent.

[0071] However, the existing preparation method of single-crystal materials has the technical defect of complicated process. The positive electrode material prepared by the preparation method is applied to sodium secondary batteries, and the cycle life of the battery is not ideal.

[0072] To solve the above technical problems, the present application discloses a sodium secondary battery, which comprises a positive electrode sheet, a separator and a negative electrode sheet stacked together. The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer on at least one side surface of the positive electrode current collector. The positive electrode film layer comprises a positive electrode active material, which comprises single-crystal particles and / or single-crystal-like particles of layered transition metal oxides. The single-crystal particles and / or single-crystal-like particles comprise any one or more of spherical, spherical-like, polygonal sheet-shaped and polygonal columnar shapes.

[0073] The positive electrode active material satisfies the following conditions:

[0074] (1) The volume particle size distribution Dv50 is 3-7 μm;

[0075] (2) The specific surface area BET is 0.3-0.5 m 2 / g. 2 .

[0076] The positive electrode active material provided by the present application contains single-crystal particles and / or single-crystal-like particles, which are beneficial to improving the cycle life of sodium secondary batteries in secondary batteries.

[0077] Therefore, the sodium secondary battery provided by the present application is beneficial to improve the cycle life of the battery, and at the same time, is beneficial to improve the energy density of the battery, thereby increasing the user experience. The sodium secondary battery can include an outer package. The outer package can be used to package the electrode assembly and the electrolyte composed of the above-mentioned sodium secondary battery. The outer package of the sodium secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the sodium secondary battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, and as plastic, it includes but is not limited to polypropylene, polybutylene terephthalate, and polybutylene succinate, etc.

[0078] The shape of the sodium secondary battery according to the present application is not particularly limited, and it can be cylindrical, square or any other shape. For example, FIG. 1 is a sodium secondary battery (secondary battery 10) in a square structure as an example.

[0079] According to some embodiments of the present application, referring to FIG. 2, the outer package can include a shell 101 and a cover plate 103. The shell 101 can include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 101 has an opening communicating with the receiving cavity, and the cover plate 103 can be arranged on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the separator can form an electrode assembly 102 through a winding process or a stacking process. The electrode assembly 102 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 102. The number of electrode assemblies 102 contained in the secondary battery 10 can be one or more, which can be selected by those skilled in the art according to specific actual needs.

[0080] The electrode assembly 102 provided by the present application applied to the secondary battery is beneficial to improve the performance of the secondary battery, which can be used as a power supply of an electric device, or as an energy storage unit of an electric device, and the electric device is applied to the field of power, such as mobile devices (such as mobile phones, notebook computers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited to the above-mentioned fields.

[0081] Some embodiments of the present application take a vehicle as an example for convenience of illustration.

[0082] Please refer to FIG. 3, which is a structural schematic diagram of a vehicle 10000 according to some embodiments of the present application. The vehicle 10000 can be a fuel automobile, a gas automobile, or a new energy automobile, and the new energy automobile can be a pure electric automobile, a hybrid automobile, or a range extended automobile, etc. The vehicle 10000 is internally provided with a battery 1000, which can be arranged at the bottom, the head, or the tail of the vehicle 10000. The battery 1000 can be used for power supply of the vehicle 10000, for example, the battery 1000 can be used as an operating power source of the vehicle 10000. The vehicle 10000 can further include a controller 2000 and a motor 3000, and the controller 2000 is used to control the battery 1000 to supply power to the motor 3000, for example, to meet the working power demand of the vehicle 10000 during starting, navigation, and driving.

[0083] In some embodiments of the present application, the battery 1000 can not only be used as an operating power source of the vehicle 10000, but also be used as a driving power source of the vehicle 10000, to replace or partially replace fuel or natural gas to provide driving power for the vehicle 10000.

[0084] Please refer to FIG. 4, which is an exploded view of the battery 1000 according to some embodiments of the present application. The battery 1000 includes a box body 200 and a battery cell 100, and the conventional battery cell includes a primary battery or a secondary battery. The present application specifically protects a secondary battery 100, which is accommodated in the box body 200. The box body 200 is used to provide an accommodation space for the battery cell 100, and the box body 200 can adopt various structures.

[0085] In some embodiments, the box body 200 can include a first part 210 and a second part 220, and the first part 210 and the second part 220 are mutually covered. The first part 210 and the second part 220 jointly define an accommodation space for accommodating the secondary battery 100. The second part 220 can be a hollow structure with one end open, and the first part 210 can be a plate-shaped structure. The first part 210 is covered on the open side of the second part 220, so that the first part 210 and the second part 220 jointly define the accommodation space. The first part 210 and the second part 220 can also be hollow structures with one side open, and the open side of the first part 210 is covered on the open side of the second part 220. Of course, the box body 200 formed by the first part 210 and the second part 220 can have various shapes, such as a cylinder, a cuboid, etc.

[0086] In the battery 1000, the battery cell 100 can be multiple, and the multiple battery cells 100 can be connected in series or in parallel or in a mixed manner, and the mixed manner refers to that the multiple battery cells 100 are connected in series and in parallel. The multiple battery cells 100 can be directly connected in series or in parallel or in a mixed manner, and then the whole of the multiple battery cells 100 is accommodated in the box body 200; of course, the battery 1000 can also be that the multiple battery cells 100 are first connected in series or in parallel or in a mixed manner to form a battery 1000 module, and then the multiple batteries 1000 modules are connected in series or in parallel or in a mixed manner to form a whole and are accommodated in the box body 200. The battery 1000 can also include other structures, for example, the battery 1000 can also include a current collection component for realizing the electrical connection between the multiple battery cells 100.

[0087] Sodium secondary battery

[0088] The present application discloses a sodium secondary battery in some embodiments, which comprises a positive electrode sheet, a separator film and a negative electrode sheet, wherein the positive electrode sheet, the separator film and the negative electrode sheet are sequentially stacked together to form the sodium secondary battery by a winding or stacking process. The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer located on at least one side surface of the positive electrode current collector, the positive electrode film layer comprises a positive electrode active material, the positive electrode active material comprises single crystal particles and / or single crystal-like particles of layered transition metal oxides; the single crystal particles and / or single crystal-like particles comprise any one or more of spherical, spherical-like, polygonal flaky, polygonal columnar shapes;

[0089] and the above-mentioned positive electrode active material satisfies the following conditions:

[0090] (1) the volume particle size distribution Dv50 is 3 μm-7 μm;

[0091] (2) the specific surface area BET is 0.3 m 2 / g-0.5 m 2 / g.

[0092] The positive electrode sheet, the separator film and the negative electrode sheet in the present application can be formed into a secondary battery by a winding or stacking process. Specifically, the present application illustrates a secondary battery 10 formed by a stacking method in FIG. 5, and it can be known from FIG. 5 that the negative electrode sheet 1 or the positive electrode sheet 2 is placed between the adjacent two separator films 3, and the negative electrode sheet 1 and the positive electrode sheet 2 are sequentially and alternately arranged along the stacking direction (the coordinate axis x direction). The number and size of the negative electrode sheet 1 and / or the positive electrode sheet 2 can be selected according to the actual situation, and the present application will not be described here. And the present application only illustrates one stacking method in FIG. 5, and other stacking or winding methods are also within the protection scope of the present application.

[0093] As shown in FIGS. 6A and 6B, the positive electrode tab 2 includes a positive electrode current collector 21 and a positive electrode film layer 22 located on at least one side surface of the positive electrode current collector 21. FIG. 6B shows that the positive electrode film layer 22 is arranged on either side surface of the positive electrode current collector 21, and FIG. 6A shows that the positive electrode film layer 22 is arranged on both side surfaces of the positive electrode current collector 21. The formation of the positive electrode film layer 22 on the surface of the positive electrode current collector 21 includes any method in the art, such as coating, deposition, etc.

[0094] The single crystal particle in the present application refers to a single particle or primary particle with a complete crystal shape (perfect crystal edges and crystal faces), and the crystal lattice inside the particle is periodically arranged.

[0095] The single crystal particle in the present application refers to a single particle or primary particle with a complete crystal shape (perfect crystal edges and crystal faces), and the crystal lattice inside the particle is periodically arranged.

[0096] The shape of the single crystal particle and / or the single crystal-like particle in the present application is the shape obtained by observing the electron microscope image of the positive electrode active material with the naked eye. Among them, the polygon refers to at least a quadrilateral and above.

[0097] The single crystal particle and / or the single crystal-like particle provided in the present application have suitable particle size and specific surface area, and thus are beneficial to improve the cycle life of the sodium secondary battery.

[0098] The measurement method of the volume particle size distribution Dv50 of the positive electrode active material in the present application includes: referring to GB / T19077-2016 to obtain the volume particle size distribution curve of the positive electrode active material, and taking the particle size corresponding to the cumulative volume distribution percentage of 50% as the average particle size Dv50. The test instrument can be a Mastersizer3000 type laser particle size analyzer of Malvern Instruments Ltd., UK. Among them, deionized water is used as the solvent, and the positive electrode active material is ultrasonically treated for 5 min before testing.

[0099] In some embodiments of the present application, the volume particle size distribution Dv50 of the positive electrode active material includes any one of 3.0 μm, 3.1 μm, 3.2 μm, 3.3 μm, 3.4 μm, 3.5 μm, 3.6 μm, 3.7 μm, 3.8 μm, 3.9 μm, 4.0 μm, 4.1 μm, 4.2 μm, 4.3 μm, 4.4 μm, 4.5 μm, 4.6 μm, 4.7 μm, 4.8 μm, 4.9 μm, 5.0 μm, 5.1 μm, 5.2 μm, 5.3 μm, 5.4 μm, 5.5 μm, 5.6 μm, 5.7 μm, 5.8 μm, 5.9 μm, 6.0 μm, 6.1 μm, 6.2 μm, 6.3 μm, 6.4 μm, 6.5 μm, 6.6 μm, 6.7 μm, 6.8 μm, 6.9 μm, 7.0 μm or satisfies any one of the above range values.

[0100] The measurement method of the surface area BET of the positive electrode active material provided in the present application comprises: referring to GB / T 19587-2004, using the nitrogen adsorption specific surface area analysis test method for testing, and using the BET (Brunauer Emmett Teller) method to calculate the specific surface area of the positive electrode active material. The testing instrument can be a TRISTAR II 3020 type specific surface area and porosity analyzer of the Micromeritics company in the United States.

[0101] In some embodiments of the present application, the specific surface area BET of the positive electrode active material comprises any one of 0.30 m 2 / g, 0.31 m 2 / g, 0.32 m 2 / g, 0.33 m 2 / g, 0.34 m 2 / g, 0.35 m 2 / g, 0.36 m 2 / g, 0.37 m 2 / g, 0.38 m 2 / g, 0.39 m 2 / g, 0.40 m 2 / g, 0.41 m 2 / g, 0.42 m 2 / g, 0.43 m 2 / g, 0.44 m 2 / g, 0.45 m 2 / g, 0.46 m 2 / g, 0.47 m 2 / g, 0.48 m 2 / g, 0.49 m 2 / g, 0.50 m 2 / g, or satisfies any one of the above range values.

[0102] The single crystal particles and / or quasi-single crystal particles provided in the present application have suitable particle size and specific surface area, so that the probability of interface side reaction can be reduced to a certain extent, and therefore the cycle service life of the sodium secondary battery is improved.

[0103] At the same time, the single crystal particles and / or quasi-single crystal particles provided in the present application can also load higher voltage, and are also beneficial to improve the energy density of the battery.

[0104] In some embodiments of the present application, the mass percentage content of the single crystal particles in the above positive electrode active material is 20% to 40%.

[0105] The method for measuring the mass percentage content of single crystal particles in the positive electrode active material in the present application comprises obtaining part of the positive electrode active material in the positive electrode film layer, weighing m0, separating the single crystal particles in the positive electrode active material under a high-power electron microscope, weighing m1, and calculating (m1 ÷ m0) × 100% to obtain the mass percentage content of the single crystal particles in the positive electrode active material.

[0106] The present application discloses in these embodiments that the mass percentage content of single crystal particles in the above-mentioned positive electrode active material comprises any one of 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40% or any one of the above-mentioned range values.

[0107] In some embodiments of the present application, the mass percentage content of single crystal particles in the above-mentioned positive electrode active material is 60% to 80%.

[0108] The method for measuring the mass percentage content of single crystal particles in the positive electrode active material in the present application comprises obtaining part of the positive electrode active material in the positive electrode film layer, weighing m0, separating the single crystal particles in the positive electrode active material under a high-power electron microscope, weighing m1, and calculating (m1 ÷ m0) × 100% to obtain the mass percentage content of the single crystal particles in the positive electrode active material.

[0109] The present application discloses in these embodiments that the mass percentage content of single crystal particles in the above-mentioned positive electrode active material is 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80% or any one of the above-mentioned range values.

[0110] Some embodiments of the present application disclose that the positive electrode active material comprises single crystal particles and quasi-single crystal particles, and the sum of the mass percentage content of the single crystal particles and the mass percentage content of the quasi-single crystal particles is less than or equal to 100%.

[0111] In some embodiments of the present application, the volume particle size distribution Dv50 of the single crystal particles is 5 μm to 7 μm.

[0112] As described above, the single crystal particles are separated out, and then the volume particle size distribution curve of the single crystal particles is obtained by referring to GB / T 19077-2016, and the particle size corresponding to the cumulative volume distribution percentage of 50% is taken as the average particle size Dv50.

[0113] In some embodiments of the present application, the volume particle size distribution Dv50 of the single crystal particles is 3-5 μm, not including 5 μm.

[0114] In some embodiments of the present application, the volume particle size distribution Dv50 of the single crystal particles is 3-5 μm, not including 5 μm.

[0115] As described above, the single crystal-like particles are separated out, and then the volume particle size distribution curve of the single crystal-like particles is obtained by referring to GB / T 19077-2016, and the particle size corresponding to the cumulative volume distribution percentage of 50% is taken as the average particle size Dv50.

[0116] In some embodiments of the present application, the volume particle size distribution Dv50 of the single crystal particles is 3-5 μm, not including 5 μm.

[0117] In some embodiments of the present application, the chemical formula of the layered transition metal oxide is Na x M y O z , wherein M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, 0

[0118] In some embodiments of the present application, the layered transition metal oxide is a nickel-iron-manganese-based layered transition metal oxide, and the chemical formula of the nickel-iron-manganese-based layered transition metal oxide is NaNi a Fe b Mn c M1 d O2, wherein a+b+c+d=1, 0≤a≤1, 0≤b≤1, 0≤c≤1, 0≤d≤1, and M1 is selected from one or more of Co, Cr, V, Al, Sn, B, Cu, Fe, Li, Ti, Mg or Zn.

[0119] The present application discloses in these embodiments that a, b, c, d are each independently selected from any one of 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 0.98, 1.0 or any one of the above range values.

[0120] The present application discloses in some embodiments that M1 is selected from one or more of Co, Al, Fe.

[0121] In some embodiments of the present application, the compaction density of the positive electrode film layer is 3.0g / cm 3 ~3.4g / cm 3 .

[0122] The compaction density of the positive electrode film layer of the present application can be used to characterize the energy density of the material, the compaction density of the positive electrode film layer = the area density of the positive electrode film layer / the thickness of the positive electrode film layer, the thickness of the positive electrode film layer includes the distance between the two end faces of the positive electrode film layer along the thickness direction, the area density of the positive electrode film layer = the weight of the single-sided positive electrode film layer / the area of the single-sided positive electrode film layer, wherein the weight of the single-sided positive electrode film layer can be obtained by weighing, and the area of the single-sided positive electrode film layer can be obtained according to the area calculation formula according to the shape of the film layer. The present application mainly discusses the compaction density of the positive electrode film layer after formation and before recycling here, and those skilled in the art know that the compaction density of the positive electrode film layer will decrease with the use of the battery, and it is possible to be as low as 3.0g / cm 3 .

[0123] The compaction density of the positive electrode film layer of the present application is 3.0g / cm 3 ~3.4g / cm 3 to illustrate that the energy density of the sodium secondary battery of the present application is relatively high.

[0124] The present application discloses in these embodiments that the compaction density of the positive electrode film layer includes any one of 3.0g / cm 3 , 3.1g / cm 3 , 3.2g / cm 3 , 3.3g / cm 3 , 3.4g / cm 3 or any one of the above range values.

[0125] In some embodiments of the present application, the sodium secondary battery further comprises an electrolyte, which can be in a liquid state, a solid state, or a gel state. Among them, the solid state is a solid electrolyte, the liquid state is a liquid electrolyte, and the gel state is a gel electrolyte. The sodium secondary battery of the present application uses a liquid electrolyte, that is, an electrolyte. The electrolyte contains an organic solvent. The organic solvent contains any one or more of carboxylic acid ester compounds, carbonate compounds, and ether compounds. Among them, the carboxylic acid ester compounds contain one or more of ethyl acetate (EA), methyl acetate (MA), ethyl propionate (EP), propyl acetate (PA), methyl propionate (MP), methyl butyrate (MB), ethyl butyrate (EB), and 1,4-butyrolactone (GBL); the carbonate compounds contain one or more of ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl ethyl carbonate (EMC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), and fluoroethylene carbonate (FEC). The ether compounds include at least one of tetrahydrofuran, dimethyl tetrahydrofuran, tetrahydropyran, dimethyl tetrahydropyran, 1,2-dimethoxyethane, dipropylene glycol dimethyl ether, or dimethyl phthalate. The organic solvent of the present application further contains one or both of a nitrile solvent and a sulfone solvent, the nitrile solvent contains one or more of acetonitrile (AN), glutaronitrile (GLN), and adiponitrile (ADN). The sulfone solvent contains at least one or a combination of two of sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0126] According to some embodiments of the present application, the electrolyte further comprises a film-forming stabilizer, which comprises a positive electrode film-forming stabilizer and a negative electrode film-forming stabilizer. The positive electrode film-forming stabilizer comprises a carbonate additive and / or a sulfate additive. The carbonate additive comprises one or more of vinylene carbonate (VC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), vinyl ethylene carbonate (VEC), and dioctyl carbonate (CC). The sulfate additive comprises a cyclic sulfonate additive and / or a hydrocarbon sulfonate additive. The cyclic sulfonate additive comprises one or more of 1,3-propane sultone (PS), propene sultone (PES), and 3-fluoro-1,3-propane sultone (FPS). The hydrocarbon sulfonate additive comprises one or more of vinyl sulfonate (DTD), diethyl sulfonate (DES), and dimethyl sulfonate (DMS). The negative electrode film-forming stabilizer comprises one or more of a boron-containing sodium salt, a phosphorus-containing sodium salt, and a sulfur-containing sodium salt. The boron-containing sodium salt comprises one or more of sodium tetrafluoroborate (NaBF4), sodium bis(oxalato)borate (NaBOB), and sodium bis(fluoro oxalato)borate (NaDFOB). The phosphorus-containing sodium salt comprises one or more of sodium difluorophosphate (NaPO2F2), sodium fluorophosphate (Na2PO3F), and sodium phosphate (Na3PO4). The sulfur-containing sodium salt comprises one or more of sodium fluorosulfonate (NaFSO3), sodium sulfate (Na2SO4), and sodium sulfamate (NaSO3NH2).

[0127] [Positive electrode tab]

[0128] According to some embodiments of the present application, as described above, the positive electrode tab comprises a positive electrode current collector and a positive electrode film layer located on at least one side surface of the positive electrode current collector. The positive electrode tab comprises a positive electrode current collector and a positive electrode film layer located on at least one side surface of the positive electrode current collector. The positive electrode film layer comprises a positive electrode active material, which comprises single crystal particles and / or single crystal-like particles of a layered transition metal oxide. The single crystal particles and / or single crystal-like particles comprise any one or more of spherical, spherical-like, polygonal flake, and polygonal columnar shapes.

[0129] The positive electrode active material satisfies the following conditions:

[0130] (1) The volume particle size distribution Dv50 is 3 μm to 7 μm;

[0131] (2) The specific surface area BET is 0.3 m 2 / g to 0.5 m 2 / g.

[0132] In the present application, the single crystal particle refers to a single particle or primary particle having a complete crystal shape (perfect crystal edges and crystal faces). The crystal lattice inside the particle is periodically arranged.

[0133] The quasi-single crystal particles in the present application refer to irregularly shaped particles formed by aggregation of a small amount of large particle size single crystal particles.

[0134] The shape of the single crystal particles and / or quasi-single crystal particles in the present application is the shape obtained by observing an electron microscope image of the positive electrode active material with the naked eye. Among them, the polygon refers to at least quadrilateral and above.

[0135] The single crystal particles and / or quasi-single crystal particles provided in the present application have higher structural stability, and thus are beneficial to improve the cycle service life of the sodium secondary battery.

[0136] The measurement method of the volume particle size distribution Dv50 of the positive electrode active material in the present application includes: referring to GB / T 19077-2016, obtaining the volume particle size distribution curve of the single crystal particles and / or quasi-single crystal particles, and taking the particle size corresponding to the cumulative volume distribution percentage of 50% as the average particle size Dv50. The test instrument can be a Mastersizer 3000 type laser particle size analyzer of Malvern Instruments Ltd., UK. Among them, deionized water is used as the solvent, and the single crystal particles and / or quasi-single crystal particles are ultrasonically treated for 5 min before testing.

[0137] In some embodiments of the present application, the volume particle size distribution Dv50 of the positive electrode active material includes any one of 3.0 μm, 3.1 μm, 3.2 μm, 3.3 μm, 3.4 μm, 3.5 μm, 3.6 μm, 3.7 μm, 3.8 μm, 3.9 μm, 4.0 μm, 4.1 μm, 4.2 μm, 4.3 μm, 4.4 μm, 4.5 μm, 4.6 μm, 4.7 μm, 4.8 μm, 4.9 μm, 5.0 μm, 5.1 μm, 5.2 μm, 5.3 μm, 5.4 μm, 5.5 μm, 5.6 μm, 5.7 μm, 5.8 μm, 5.9 μm, 6.0 μm, 6.1 μm, 6.2 μm, 6.3 μm, 6.4 μm, 6.5 μm, 6.6 μm, 6.7 μm, 6.8 μm, 6.9 μm, 7.0 μm or satisfies any one of the above range values.

[0138] The measurement method of the specific surface area BET of the positive electrode active material in the present application includes: referring to GB / T 19587-2004, testing by using the nitrogen adsorption specific surface area analysis test method, and calculating the specific surface area of the positive electrode active material by using the BET (Brunauer Emmett Teller) method. The test instrument can be a TRISTAR II 3020 type specific surface area and porosity analyzer of Micromeritics Company, USA.

[0139] In some embodiments of the present application, the specific surface area BET of the positive electrode active material includes 0.30 m 2 / g, 0.31 m 2 / g, 0.32 m 2 / g, 0.33 m 2 / g, 0.34 m 2 / g, 0.35 m 2 / g, 0.36 m 2 / g, 0.37 m 2 / g, 0.38 m 2 / g, 0.39 m 2 / g, 0.40 m 2 / g, 0.41 m 2 / g, 0.42 m 2 / g, 0.43 m 2 / g, 0.44 m 2 / g, 0.45 m 2 / g, 0.46 m 2 / g, 0.47 m 2 / g, 0.48 m 2 / g, 0.49 m 2 / g, 0.50 m 2 / g, or any of the above range values.

[0140] The single crystal particles and / or quasi-single crystal particles provided in the present application have a suitable specific surface area to particle size, thus can reduce the probability of interface side reactions to a certain extent, and thus are beneficial to improving the cycle service life of sodium secondary batteries.

[0141] At the same time, the single crystal particles and / or quasi-single crystal particles provided in the present application can also be loaded with higher voltage, and are also beneficial to improving the energy density of the battery.

[0142] In some embodiments of the present application, the mass percentage content of the single crystal particles in the above positive electrode active material is 20% to 40%.

[0143] The method for measuring the mass percentage content of the single crystal particles in the positive electrode active material in the present application comprises obtaining part of the positive electrode active material in the positive electrode film layer, weighing m0, separating the single crystal particles in the positive electrode active material under a high-power electron microscope, weighing m1, and calculating (m1 ÷ m0) x 100% to obtain the mass percentage content of the single crystal particles in the positive electrode active material.

[0144] The present application discloses in these embodiments that the mass percentage content of the single crystal particles in the above positive electrode active material comprises any of 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, or any of the above range values.

[0145] In some embodiments of the present application, the mass percentage content of the quasi-single crystal particles in the above-mentioned positive electrode active material is 60% to 80%.

[0146] The method for measuring the mass percentage content of the quasi-single crystal particles in the positive electrode active material in the present application comprises obtaining part of the positive electrode active material in the positive electrode film layer, weighing m0, separating the quasi-single crystal particles in the positive electrode active material under a high-power electron microscope, weighing m2, and calculating (m2 ÷ m0) × 100% to obtain the mass percentage content of the single crystal particles in the positive electrode active material.

[0147] In these embodiments of the present application, the mass percentage content of the quasi-single crystal particles in the above-mentioned positive electrode active material is any one of 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80% or any one of the above-mentioned range values.

[0148] In some embodiments of the present application, the positive electrode active material comprises single crystal particles and quasi-single crystal particles, and the sum of the mass percentage content of the single crystal particles and the mass percentage content of the quasi-single crystal particles is less than or equal to 100%.

[0149] In some embodiments of the present application, the volume particle size distribution Dv50 of the single crystal particles is 5 μm to 7 μm.

[0150] As described above, the single crystal particles are separated out, and then the volume particle size distribution curve of the single crystal particles is obtained by referring to GB / T 19077-2016, and the particle size corresponding to the cumulative volume distribution percentage of 50% is taken as the average particle size Dv50.

[0151] In these embodiments of the present application, the volume particle size distribution Dv50 of the single crystal particles comprises any one of 5.0 μm, 5.1 μm, 5.2 μm, 5.3 μm, 5.4 μm, 5.5 μm, 5.6 μm, 5.7 μm, 5.8 μm, 5.9 μm, 6.0 μm, 6.1 μm, 6.2 μm, 6.3 μm, 6.4 μm, 6.5 μm, 6.6 μm, 6.7 μm, 6.8 μm, 6.9 μm, 7.0 μm or any one of the above-mentioned range values.

[0152] In some embodiments of the present application, the volume particle size distribution Dv50 of the quasi-single crystal particles is 3 μm to 5 μm and does not include 5 μm.

[0153] As described above, the quasi-single crystal particles are separated, and then a volume particle size distribution curve of the quasi-single crystal particles is obtained according to GB / T 19077-2016, and a particle size corresponding to a cumulative volume distribution percentage of 50% is taken as an average particle size Dv50.

[0154] The present application discloses in these embodiments that the volume particle size distribution Dv50 of the quasi-single crystal particles comprises any one of 3.0 μm, 3.1 μm, 3.2 μm, 3.3 μm, 3.4 μm, 3.5 μm, 3.6 μm, 3.7 μm, 3.8 μm, 3.9 μm, 4.0 μm, 4.1 μm, 4.2 μm, 4.3 μm, 4.4 μm, 4.5 μm, 4.6 μm, 4.7 μm, 4.8 μm, 4.9 μm or satisfies any one of the above range values.

[0155] In some embodiments of the present application, the chemical formula of the above-mentioned layered transition metal oxide is Na x M y O z , wherein M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, 0 < x ≤ 1, 0 < y ≤ 1, 1 < z ≤ 2.

[0156] The present application discloses in some embodiments that the above-mentioned layered transition metal oxide is a nickel-iron-manganese-based layered transition metal oxide, and the chemical formula of the nickel-iron-manganese-based layered transition metal oxide is NaNi a Fe b Mn c M1 d O2, wherein a+b+c+d = 1, 0 ≤ a ≤ 1, 0 ≤ b ≤ 1, 0 ≤ c ≤ 1, 0 ≤ d ≤ 1, and M1 is selected from one or more of Co, Cr, V, Al, Sn, B, Cu, Fe, Li, Ti, Mg or Zn.

[0157] The present application discloses in these embodiments that a, b, c and d are each independently selected from any one of 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 0.98, 1.0 or satisfies any one of the above range values.

[0158] In some embodiments of the present application, the compaction density of the positive electrode film layer is 3.0 g / cm 3 ~ 3.4 g / cm 3 .

[0159] The compaction density of the positive electrode film layer of the present application can be used to represent the energy density of the material, the compaction density of the positive electrode film layer = the areal density of the positive electrode film layer / the thickness of the positive electrode film layer, the thickness of the positive electrode film layer includes the distance between the two end faces of the positive electrode film layer along the thickness direction, the areal density of the positive electrode film layer = the weight of the single-sided positive electrode film layer / the area of the single-sided positive electrode film layer, wherein the weight of the single-sided positive electrode film layer can be obtained by weighing, and the area of the single-sided positive electrode film layer can be obtained according to the area calculation formula according to the shape of the film layer.

[0160] The compaction density of the positive electrode film layer of the present application is 3.0 g / cm 3 ~ 3.4 g / cm 3 It is illustrated that the energy density of the sodium secondary battery of the present application is relatively high.

[0161] The present application discloses the compaction density of the positive electrode film layer in these embodiments includes any one of 3.0 g / cm 3 , 3.1 g / cm 3 , 3.2 g / cm 3 , 3.3 g / cm 3 , 3.4 g / cm 3 or satisfies any one of the above range values.

[0162] In some embodiments of the present application, the positive electrode active material comprises at least one of a polyanion compound, a Prussian blue compound in addition to the above-mentioned layered transition metal oxide. Among them, the polyanion compound includes sodium vanadium trifluorophosphate (Na3V2(PO4)2F3), sodium vanadium fluorophosphate (NaVPO4F), sodium vanadium phosphate (Na3V2(PO4)3), Na4Fe3(PO4)2P2O7, NaFePO4, and one or more of the above. The Prussian blue compound is Na x M1M2(CN)6, wherein M1, M2 are one or more of Fe, Mn, Co, Ni, Cu, Zn, Cr, Ti, V, Zr, Ce, and 0 < x ≤ 2.

[0163] In some embodiments of the present application, the positive electrode film layer comprises a conductive agent, a binder, etc. in addition to the above-mentioned positive electrode active material. The conductive agent includes but is not limited to one or more of graphite, superconducting carbon, carbon black (such as acetylene black, ketjen black, Super P, etc.), carbon dots, carbon nanotubes, graphene and carbon nanofibers in combination. The binder includes but is not limited to one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorine-containing acrylate resin, styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, carboxymethyl chitosan, etc.

[0164] In some embodiments of the present application, the positive electrode current collector in the present application can be a metal foil or a composite current collector, wherein the metal foil can be an aluminum foil, and the composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material, such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc. on a polymer material base material such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0165] The forming method of the positive electrode film layer of the present application includes uniformly mixing the above-mentioned raw materials in a certain mass ratio with a solvent (such as N-methyl pyrrolidone) to form a positive electrode slurry, uniformly coating the positive electrode slurry on both sides of the positive electrode current collector; controlling the single-sided coating weight to be 0.25 g-0.50 g / 1540.25 mm 2 ; after drying, using a cold press to compact to a certain compaction density (3.0 g / cm 3 -3.4 g / cm 3 ), thereby obtaining a positive electrode sheet containing a positive electrode film layer.

[0166] [Negative electrode sheet]

[0167] According to some embodiments of the present application, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer located on at least one side surface of the negative electrode current collector. The negative electrode film layer contains a negative electrode active material.

[0168] The negative electrode active material in the present application contains a carbonaceous material, which contains one or more than two combinations of artificial graphite, natural graphite, soft carbon, and hard carbon. The artificial graphite, natural graphite, soft carbon, and hard carbon contain any form of material in the art, and any manufacturer and model in the art. At the same time, the negative electrode active material can also contain a silicon-based material, which contains one or both of silicon-oxygen material or silicon-carbon material. In addition, the negative electrode active material can also contain silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, TiO2-Li4Ti5O 12 , Li-Al alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for sodium secondary batteries can also be used. These negative electrode active materials can be used alone or in combination with two or more.

[0169] The method for preparing artificial graphite in the present application comprises: providing raw materials, performing powder shaping → granulation → graphitization treatment → performing surface roughening treatment, to obtain artificial graphite materials. The raw materials in the embodiments of the present application can use one or more of green coke, calcined coke; preferably, the raw materials include one or more of needle-shaped green petroleum coke, non-needle-shaped green petroleum coke, needle-shaped coal-based green coke, non-needle-shaped coal-based green coke, calcined needle-shaped coke, calcined petroleum coke. The powdering of the present application can be performed by using devices and methods known in the art, for example, using an air flow pulverizer, a mechanical pulverizer or a roller mill. During the crushing process, a large number of too small particles are usually generated, and sometimes too large particles are also generated. Therefore, after powdering, classification can be performed as needed to remove too small particles and too large particles in the powder after powdering. After classification, a particle product with a good particle size distribution can be obtained to facilitate the subsequent molding and / or granulation process. Classification can be performed by using devices and methods known in the art, for example, a classification screen, a gravity classifier or a centrifugal classifier. The shaping of the present application can be performed by using equipment (such as a molding machine or other molding equipment) and methods known in the art. For example, the edges and corners of the obtained particle product are polished to facilitate subsequent operations and to make the obtained product have higher stability. The granulation of the present application comprises using devices known in the art, such as a granulator, to perform granulation. The granulator usually includes a stirring reactor and a temperature control module of the reactor. In addition, the volume median particle size of the obtained product can be controlled by adjusting the process conditions in the granulation process, such as stirring speed, heating speed, granulation temperature and cooling speed. The graphitization treatment of the present application comprises high-temperature graphitization treatment and low-temperature graphitization treatment. In some embodiments, any one or both of the high-temperature graphitization treatment and the low-temperature graphitization treatment can be appropriately selected for treatment according to actual specific needs. Or the high-temperature graphitization treatment and / or the low-temperature graphitization treatment can be repeated. By high-temperature graphitization treatment, graphite with appropriate graphitization degree and graphite interlayer spacing can be obtained. Graphite prepared at an appropriate graphitization temperature can obtain appropriate graphitization degree and graphite interlayer spacing, so that the composite artificial graphite has higher structural stability and specific capacity. The surface roughening treatment of the present application comprises using conventional treatment methods in the art, such as using physical methods.

[0170] The negative electrode film layer of the present application comprises, in addition to the negative electrode active material, a binder, a conductive agent, a dispersing agent, etc. The binder comprises, but is not limited to, polyvinyl alcohol, polyethylene glycol, sodium carboxymethyl cellulose, polyethylene oxide, polyacrylic acid, polyacrylamide, sodium alginate, butadiene-styrene rubber (SBR), etc. The conductive agent comprises any kind of conventional agent in the art, such as one or more than two kinds of combination of graphite, superconducting carbon, carbon black (e.g. acetylene black, ketjen black, Super P, etc.), carbon dots, carbon nanotubes, graphene and carbon nanofibers. The dispersing agent also comprises any kind of conventional agent in the art, such as cellulose and its salts, specifically comprising, but not limited to, methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, etc.

[0171] The forming method of the negative electrode film layer of the present application comprises mixing the above-mentioned raw materials in a certain mass ratio with a solvent (e.g. deionized water) to form a negative electrode slurry, degassing the negative electrode slurry, and then uniformly coating the negative electrode slurry on both sides of the negative electrode current collector; the single-side coating weight is controlled to be 0.13 g-0.25 g / 1540.25 mm 2 ; drying, and compacting to a certain compacted density (1.65 g / cm 3 ≤ compacted density ≤ 2.0 g / cm 3 ) using a cold press, to obtain a negative electrode tab comprising a negative electrode film layer.

[0172] [Electrolyte]

[0173] In some embodiments of the present application, the sodium secondary battery further comprises an electrolyte, which can be in a liquid state, a solid state, or a gel state. Among them, the solid state is a solid electrolyte, the liquid state is a liquid electrolyte, and the gel state is a gel electrolyte. The sodium secondary battery of the present application uses a liquid electrolyte, that is, an electrolyte. The electrolyte comprises an electrolyte salt and an organic solvent. Among them, the type of electrolyte salt comprises any type of conventional in the art, such as, including but not limited to inorganic metal salts, such as NaClO4, NaAsF6, NaPF6, NaBF4, NaSbF6, NaSO3F, NaN(FSO2)2, etc.; fluorine-containing organic metal salts, such as NaCF3SO3, NaN(FSO2)(CF3SO2), NaN(CF3SO2)2, NaN(C2F5SO2)2, sodium cyclic 1,3-hexafluoropropylene disulfonimide, sodium cyclic 1,2-tetrafluoroethane disulfonimide, NaN(CF3SO2)(C4F9SO2), NaC(CF3SO2)3, NaPF4(CF3)2, NaPF4(C2F5)2, NaPF4(CF3SO2)2, NaPF4(C2F5SO2)2, NaBF2(CF3)2, NaBF2(C2F5)2, NaBF2(CF3SO2)2, NaBF2(C2F5SO2)2, etc.; and dicarboxylic acid complex metal salts, such as sodium bis(oxalato)borate, sodium difluoro(oxalato)borate, sodium tris(oxalato)phosphate, sodium difluoro bis(oxalato)phosphate, sodium tetrafluoro(oxalato)phosphate, etc.

[0174] According to some embodiments of the present application, the concentration of the electrolyte salt in the electrolyte is 0.1 mol / L to 4 mol / L. The present application discloses in these embodiments that the concentration of the electrolyte salt is any one of 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2 mol / L, 2.2 mol / L, 2.5 mol / L, 2.8 mol / L, 3 mol / L, 3.2 mol / L, 3.5 mol / L, 3.8 mol / L, 4 mol / L or satisfies any one of the above range values. The concentration of the electrolyte salt in the electrolyte described herein is the concentration when configured, and the actual battery will consume electrolyte salt during the cycle process, resulting in a decrease in concentration.

[0175] As described above, the organic solvent comprises one or more of carboxylic acid esters, carbonates, and ethers. Specifically, the carboxylic acid esters comprise one or more of ethyl acetate (EA), methyl acetate (MA), ethyl propionate (EP), propyl acetate (PA), methyl propionate (MP), methyl butyrate (MB), ethyl butyrate (EB), and 1,4-butyrolactone (GBL); the carbonates comprise one or more of ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl ethyl carbonate (EMC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), and fluoroethylene carbonate (FEC). The ethers comprise at least one of tetrahydrofuran, dimethyl tetrahydrofuran, tetrahydropyran, dimethyl tetrahydropyran, 1,2-dimethoxyethane, dipropylene glycol dimethyl ether, or dimethyl phthalate. The organic solvents of this application further include one or two of nitrile solvents and sulfone solvents. The nitrile solvents include one or more of acetonitrile (AN), glutaronitrile (GLN), and adiponitrile (ADN). The sulfone solvents include at least one or a combination of two of sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0176] According to some embodiments of this application, the electrolyte further comprises a film-forming stabilizer, which includes a positive electrode film-forming stabilizer and a negative electrode film-forming stabilizer. The positive electrode film-forming stabilizer comprises carbonate additives and / or sulfate additives. The carbonate additives include one or more of vinylene carbonate (VC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), vinyl ethylene carbonate (VEC), and dioctyl carbonate (CC). The sulfate additives include cyclic sulfonate additives and / or sulfated hydrocarbon ester additives; further, the cyclic sulfonate additives include one or more of 1,3-propanesulfonate lactone (PS), propenesulfonate lactone (PES), and 3-fluoro-1,3-propanesulfonate lactone (FPS); the sulfated hydrocarbon ester additives include one or more of vinyl sulfate (DTD), diethyl sulfate (DES), and dimethyl sulfate (DMS). The negative electrode film-forming stabilizer comprises one or more of sodium boron salts, phosphorus-containing sodium salts, and sulfur-containing sodium salts; the sodium boron salts include one or more of sodium tetrafluoroborate (NaBF4), sodium bis(oxalato)borate (NaBOB), and sodium bis(oxalato)borate (NaDFOB); the phosphorus-containing lithium salts include one or more of sodium difluorophosphate (NaPO2F2), sodium fluorophosphate (Na2PO3F), and sodium phosphate (Na3PO4). The sulfur-containing sodium salts include one or more of sodium fluorosulfonate (NaFSO3), sodium sulfate (Na2SO4), and sodium aminosulfonate (NaSO3NH2).

[0177] [Separator]

[0178] In some embodiments of the present application, a separator is disclosed. The present application does not have a particular limitation on the type of the separator, and any known porous structure separator with good chemical stability and mechanical stability can be selected.

[0179] In some embodiments, the separator comprises a base material layer, and the base material of the base material layer comprises one or more of polyethylene, polypropylene, poly-p-phenylene terephthalamide, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, and polyamide.

[0180] In some embodiments, the separator comprises a base material layer and a coating layer arranged on the surface of the base material layer; the base material of the base material layer comprises one or more of polyethylene, polypropylene, poly-p-phenylene terephthalamide, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, and polyamide; and the coating layer comprises a ceramic coating layer and / or a polymer coating layer. The base material layer has good permeability to lithium ions, which is conducive to the migration of lithium ions; and the surface of the base material layer is provided with the coating layer, which can further improve the mechanical properties of the separator. Optionally, the ceramic particles in the ceramic coating layer comprise one or more of SiO2, Al2O3, AlOOH, CaO, TiO2, MgO, ZnO, ZrO2, Mg(OH)2, and BaSO4. Optionally, the polymer material of the polymer coating layer comprises one or more of polyethylene (PE), polypropylene (PP), poly-p-phenylene terephthalamide (PPTA), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), polyimide (PI), and polyamide (PA). The polymer coating layer and the base material layer can be made of the same or different materials, and the thickness of the polymer coating layer and the base material layer can be different. Optionally, the thickness of the polymer coating layer is less than the thickness of the base material layer.

[0181] In other embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, and there is no particular limitation. When the separator is a multi-layer composite film, the materials of the layers can be the same or different, and there is no particular limitation.

[0182] Positive electrode active material for sodium secondary battery

[0183] Disclosed in some embodiments of the present application is a positive electrode active material for a sodium secondary battery, the positive electrode active material comprising single-crystal particles and / or quasi-single-crystal particles of a layered transition metal oxide, the single-crystal particles and / or quasi-single-crystal particles comprising any one or more of a spherical shape, a quasi-spherical shape, a polygonal flake shape, and a polygonal columnar shape; the positive electrode active material satisfying the following conditions:

[0184] (1) a volume particle size distribution Dv50 of 3 μm to 7 μm;

[0185] (2) a specific surface area BET of 0.3 m 2 / g to 0.5 m 2 / g.

[0186] The single-crystal particles in the present application refer to single particles or primary particles having a complete crystal shape (perfect crystal edges and crystal faces), and the crystal lattices inside the particles are periodically arranged.

[0187] The quasi-single-crystal particles in the present application refer to irregularly shaped particles formed by aggregation of a small amount of large-diameter single-crystal particles.

[0188] The shape of the single-crystal particles and / or quasi-single-crystal particles in the present application is the shape obtained by observing an electron microscope image of the positive electrode active material with the naked eye. The polygonal shape refers to at least a quadrilateral shape and above.

[0189] The single-crystal particles and / or quasi-single-crystal particles provided in the present application have suitable particle sizes and specific surface areas, and thus are beneficial to improving the cycle life of a sodium secondary battery.

[0190] The measurement method of the volume particle size distribution Dv50 of the positive electrode active material in the present application comprises: referring to GB / T19077-2016 to obtain a volume particle size distribution curve of the single-crystal particles and / or quasi-single-crystal particles, and taking the particle size corresponding to the cumulative volume distribution percentage of 50% as the average particle size Dv50. The testing instrument can be a Mastersizer 3000 laser particle size analyzer of Malvern Instruments Ltd., UK. Deionized water is used as the solvent, and the single-crystal particles and / or quasi-single-crystal particles are ultrasonically treated for 5 min before testing.

[0191] In some embodiments of the present application, the volume particle size distribution Dv50 of the positive electrode active material comprises any one of 3.0 μm, 3.1 μm, 3.2 μm, 3.3 μm, 3.4 μm, 3.5 μm, 3.6 μm, 3.7 μm, 3.8 μm, 3.9 μm, 4.0 μm, 4.1 μm, 4.2 μm, 4.3 μm, 4.4 μm, 4.5 μm, 4.6 μm, 4.7 μm, 4.8 μm, 4.9 μm, 5.0 μm, 5.1 μm, 5.2 μm, 5.3 μm, 5.4 μm, 5.5 μm, 5.6 μm, 5.7 μm, 5.8 μm, 5.9 μm, 6.0 μm, 6.1 μm, 6.2 μm, 6.3 μm, 6.4 μm, 6.5 μm, 6.6 μm, 6.7 μm, 6.8 μm, 6.9 μm, 7.0 μm or satisfies any one of the above range values.

[0192] The measurement method of the surface area BET of the positive electrode active material of the present application comprises: referring to GB / T 19587-2004, using the nitrogen adsorption specific surface area analysis test method for testing, and using the BET (Brunauer Emmett Teller) method to calculate the specific surface area of the single crystal particles and / or single crystal-like particles. The test instrument can be a TRISTAR II 3020 type specific surface area and porosity analyzer of the Micromeritics company in the United States.

[0193] In some embodiments of the present application, the specific surface area BET of the positive electrode active material comprises any one of 0.30 m 2 / g, 0.31 m 2 / g, 0.32 m 2 / g, 0.33 m 2 / g, 0.34 m 2 / g, 0.35 m 2 / g, 0.36 m 2 / g, 0.37 m 2 / g, 0.38 m 2 / g, 0.39 m 2 / g, 0.40 m 2 / g, 0.41 m 2 / g, 0.42 m 2 / g, 0.43 m 2 / g, 0.44 m 2 / g, 0.45 m 2 / g, 0.46 m 2 / g, 0.47 m 2 / g, 0.48 m 2 / g, 0.49 m 2 / g, 0.50 m 2 / g or satisfies any one of the above range values.

[0194] The single crystal particles and / or quasi-single crystal particles provided by the application have suitable specific surface area and particle size, and thus can reduce the probability of interface side reactions to a certain extent, thereby improving the cycle service life of the sodium secondary battery.

[0195] Meanwhile, the single crystal particles and / or quasi-single crystal particles provided by the application can also support a higher voltage, and are also beneficial to improving the energy density of the battery.

[0196] In some embodiments of the application, the mass percentage content of the single crystal particles in the positive electrode active material is 20% to 40%.

[0197] The method for measuring the mass percentage content of the single crystal particles in the positive electrode active material in the application comprises the following steps: obtaining part of the positive electrode active material in the positive electrode film layer, weighing m0, separating the single crystal particles in the positive electrode active material under a high-power electron microscope, weighing m1, and calculating (m1 ÷ m0) × 100% to obtain the mass percentage content of the single crystal particles in the positive electrode active material.

[0198] In these embodiments, the application discloses that the mass percentage content of the single crystal particles in the positive electrode active material comprises any one of 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, or any one of the above range values.

[0199] In some embodiments of the application, the mass percentage content of the quasi-single crystal particles in the positive electrode active material is 60% to 80%.

[0200] The method for measuring the mass percentage content of the quasi-single crystal particles in the positive electrode active material in the application comprises the following steps: obtaining part of the positive electrode active material in the positive electrode film layer, weighing m0, separating the quasi-single crystal particles in the positive electrode active material under a high-power electron microscope, weighing m2, and calculating (m2 ÷ m0) × 100% to obtain the mass percentage content of the single crystal particles in the positive electrode active material.

[0201] In these embodiments, the application discloses that the mass percentage content of the quasi-single crystal particles in the positive electrode active material is any one of 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, or any one of the above range values.

[0202] Some embodiments of the present application disclose that the positive electrode active material comprises single crystal particles and quasi-single crystal particles, and the sum of the mass percentage content of the single crystal particles and the mass percentage content of the quasi-single crystal particles is less than or equal to 100%.

[0203] In some embodiments of the present application, the volume particle size distribution Dv50 of the single crystal particles is 5 μm to 7 μm.

[0204] As described above, the single crystal particles are separated out, and then the volume particle size distribution curve of the single crystal particles is obtained by referring to GB / T 19077-2016, and the particle size corresponding to the cumulative volume distribution percentage of 50% is taken as the average particle size Dv50.

[0205] In these embodiments, the present application discloses that the volume particle size distribution Dv50 of the single crystal particles comprises any one of 5.0 μm, 5.1 μm, 5.2 μm, 5.3 μm, 5.4 μm, 5.5 μm, 5.6 μm, 5.7 μm, 5.8 μm, 5.9 μm, 6.0 μm, 6.1 μm, 6.2 μm, 6.3 μm, 6.4 μm, 6.5 μm, 6.6 μm, 6.7 μm, 6.8 μm, 6.9 μm, 7.0 μm or satisfies any one of the above range values.

[0206] In these embodiments, the present application discloses that the specific surface area BET of the single crystal particles comprises any one of 0.30 m 2 / g, 0.31 m 2 / g, 0.32 m 2 / g, 0.33 m 2 / g, 0.34 m 2 / g, 0.35 m 2 / g, 0.36 m 2 / g, 0.37 m 2 / g, 0.38 m 2 / g, 0.39 m 2 / g, 0.40 m 2 / g or satisfies any one of the above range values.

[0207] In some embodiments of the present application, the volume particle size distribution Dv50 of the quasi-single crystal particles is 3 μm to 5 μm and does not include 5 μm.

[0208] As described above, the quasi-single crystal particles are separated out, and then the volume particle size distribution curve of the quasi-single crystal particles is obtained by referring to GB / T 19077-2016, and the particle size corresponding to the cumulative volume distribution percentage of 50% is taken as the average particle size Dv50.

[0209] The present application discloses in these embodiments that the volume particle size distribution Dv50 of the quasi-single crystal particles comprises any one of 3.0 μm, 3.1 μm, 3.2 μm, 3.3 μm, 3.4 μm, 3.5 μm, 3.6 μm, 3.7 μm, 3.8 μm, 3.9 μm, 4.0 μm, 4.1 μm, 4.2 μm, 4.3 μm, 4.4 μm, 4.5 μm, 4.6 μm, 4.7 μm, 4.8 μm, 4.9 μm or satisfies any one of the above range values.

[0210] In some embodiments of the present application, the chemical formula of the above-mentioned layered transition metal oxide is Na x M y O z , wherein M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, 0 < x ≤ 1, 0 < y ≤ 1, 1 < z ≤ 2.

[0211] The present application discloses in some embodiments that the above-mentioned layered transition metal oxide is a nickel-iron-manganese-based layered transition metal oxide, and the chemical formula of the nickel-iron-manganese-based layered transition metal oxide is NaNi a Fe b Mn c M1 d O2, wherein a + b + c + d = 1, 0 ≤ a ≤ 1, 0 ≤ b ≤ 1, 0 ≤ c ≤ 1, 0 ≤ d ≤ 1, and M1 is selected from one or more of Co, Cr, V, Al, Sn, B, Cu, Fe, Li, Ti, Mg or Zn.

[0212] The present application discloses in these embodiments that a, b, c and d are each independently selected from any one of 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 0.98, 1.0 or satisfies any one of the above range values.

[0213] In some embodiments of the present application, in addition to the above-mentioned layered transition metal oxide, the positive electrode active material further comprises at least one of a polyanion compound and a prussian blue compound. The polyanion compound includes sodium vanadium trifluorophosphate (Na3V2(PO4)2F3), sodium vanadium fluorophosphate (NaVPO4F), sodium vanadium phosphate (Na3V2(PO4)3), Na4Fe3(PO4)2P2O7, NaFePO4, or one or more of the above. The prussian blue compound is Na xM1M2(CN)6, wherein M1, M2 are one or more than two of Fe, Mn, Co, Ni, Cu, Zn, Cr, Ti, V, Zr, Ce, and 0 < x < 2.

[0214] In some embodiments of the present application, the tap density of the single crystal particles and / or quasi-single crystal particles described above is any one of 1.55 g / cm 3 ~ 1.80 g / cm 3 .

[0215] The tap density in the present application includes any concept in the art, which can be tested by using instruments or methods known in the art, such as by referring to the standard GB / T5162-2006.

[0216] The present application discloses in these embodiments that the tap density of the single crystal particles and / or quasi-single crystal particles is any one of 1.55 g / cm 3 , 1.56 g / cm 3 , 1.57 g / cm 3 , 1.58 g / cm 3 , 1.59 g / cm 3 , 1.60 g / cm 3 , 1.61 g / cm 3 , 1.62 g / cm 3 , 1.63 g / cm 3 , 1.64 g / cm 3 , 1.65 g / cm 3 , 1.66 g / cm 3 , 1.67 g / cm 3 , 1.68 g / cm 3 , 1.69 g / cm 3 , 1.70 g / cm 3 , 1.71 g / cm 3 , 1.72 g / cm 3 , 1.73 g / cm 3 , 1.74 g / cm 3 , 1.75 g / cm 3 , 1.76 g / cm 3 , 1.77 g / cm 3 , 1.78 g / cm 3 , 1.79 g / cm 3 , 1.80 g / cm 3 in the above range.

[0217] Method for preparing positive electrode active material for sodium secondary battery

[0218] The application discloses a preparation method of a positive electrode active material for a sodium secondary battery, comprising the following steps:

[0219] S1, providing a positive electrode material precursor, comprising the following preparation process:

[0220] S11, preparing a metal salt solution with a molar concentration of (2.0±0.4) mol / L according to the chemical formula Ni x1 Fe y1 Mn z1 (OH)2, wherein 0≤x1≤1, 0≤y1≤1, 0≤z1≤1, and x1+y1+z1=1, and a sodium hydroxide solution with a mass fraction of 25% to 35%, an ammonia solution with a mass fraction of 15% to 25%, and a chelating agent solution (ethylenediaminetetraacetic acid or N-hydroxyethylenediamine) with a mass fraction of 0.001% to 0.25% are prepared; deionized water is added into a reaction kettle, and then the ammonia solution, the chelating agent solution and the sodium hydroxide solution are sequentially added, the pH is controlled to be 10.3 to 12.5, and the reaction temperature is controlled to be 40 to 70 ± 1 DEG C;

[0221] S12, adding the metal salt solution, the sodium hydroxide solution, the ammonia solution and the chelating agent solution into the reaction kettle, the flow rate ratio of the four solutions is (15 to 125):(3 to 55):(1 to 7):(0.1 to 2), the nucleation is performed for 3 to 5 hours, the pH is reduced to below 11.6 by adjusting the flow rate of the sodium hydroxide solution to complete the nucleation process, and the metal salt solution, the sodium hydroxide solution, the ammonia solution and the chelating agent solution are continuously added into the reaction kettle to perform a coprecipitation reaction, the flow rate ratio of the four solutions is (15 to 125):(3 to 55):(1 to 7):(0.1 to 2), the reaction pH is controlled to be 10.3 to 11.6, and the reaction is maintained for 40 to 90 hours to complete the growth process of the precursor particles;

[0222] S13, transferring the solution in the reaction kettle into a centrifuge to perform solid-liquid separation, obtaining a positive electrode material precursor material containing water, and drying the wet precursor material at 110 to 120 DEG C for 10 to 20 hours to obtain a positive electrode material precursor finished product;

[0223] S2, preparing a positive electrode material intermediate product: mixing the positive electrode material precursor with sodium carbonate, wherein the molar amount of metal atoms in the positive electrode material precursor is N1, the molar amount of sodium atoms in the sodium carbonate is N2, and N1 / N2 is 1:(0.5 to 1.1);

[0224] The intermediate product of the cathode material is prepared by first calcining in an oxygen-containing atmosphere (such as air or pure oxygen), the first calcination temperature is 850-970℃, the holding time is 7-15h, then the temperature is decreased to room temperature, and then rough breaking, fine crushing and screening are performed to obtain the intermediate product of the cathode material, the volume particle size distribution Dv50 of the intermediate product of the cathode material is 8-12μm; the intermediate product of the cathode material contains polycrystalline particles of layered transition metal oxides; and the mass percentage content of the polycrystalline particles is about 100%. The measurement method of the mass percentage content of the polycrystalline particles includes observing the particle morphology under a high-power electron microscope, and almost all the particles are polycrystalline particles. The polycrystalline particles in the present application refer to single particles containing multiple crystal grains, and the crystal lattice of each crystal grain is periodically arranged, but the orientation of these crystal grains is random. Such crystal grains will produce some diffraction points due to the periodic structure inside, and the diffraction points appear on a circle with a radius of 1 / d, and the circle radius is different for different crystal faces, thus multiple rings are generated.

[0225] S3, preparing a cathode active material: dispersing a dispersant into a solvent to form a mixed solvent, dispersing the intermediate product of the cathode material into the mixed solvent, controlling the mass of the intermediate product of the cathode material and the volume of the mixed solvent to be (10-20g) / (20-100mL), and then heating and stirring the obtained mixture until the solvent is evaporated;

[0226] The cathode active material is prepared by second calcining in an oxygen-containing atmosphere (such as air or pure oxygen), the second calcination temperature is 600-1000℃, and the holding time is 3-24h; the cathode active material prepared in the present application contains single crystal particles and / or quasi-single crystal particles of layered transition metal oxides, and the mass percentage content of the single crystal particles and / or quasi-single crystal particles in the cathode active material is >98%; the measurement method of the mass percentage content of the single crystal particles and / or quasi-single crystal particles includes obtaining part of the cathode active material, weighing m0, and then observing the particle morphology under a high-power electron microscope. 0， The single crystal particles and quasi-single crystal particles in the cathode active material are separated out under a high-power electron microscope, weighed as m3, and the mass percentage content of the single crystal particles in the cathode active material is calculated as (m3÷m0)×100%.

[0227] In some embodiments of the present application, the dispersant satisfies the following conditions:

[0228] (1) the dispersant is soluble in one or more of alcohol solvents, acetone and water;

[0229] (2) the decomposition temperature of the dispersant is less than or equal to 600℃, and the decomposition temperature of the dispersant is the temperature corresponding to the decomposition peak of the thermogravimetric curve of the dispersant.

[0230] The method for obtaining the decomposition temperature of the dispersant of the present application comprises: taking 10-20 mg of the dispersant sample powder, drying to remove moisture, placing in a thermal analysis crucible, setting the test temperature range to 0-600℃, setting the heating rate to 10℃ / min, placing in a thermal gravimetric analyzer to obtain a thermal gravimetric analysis curve (TG curve). Then, taking the first derivative of each point on the TG curve with respect to the time coordinate to obtain a differential thermal gravimetric curve (DTG curve). The DTG curve shows the change of the thermal weight loss rate with time, and the temperature corresponding to the thermal weight loss rate greater than zero is the decomposition temperature.

[0231] The selected dispersant of the present application is convenient for dissolving with the solvent and also convenient for removing during the second calcination.

[0232] In some embodiments of the present application, the above-mentioned dispersant comprises polyvinylpyrrolidone and modified compounds thereof. The polyvinylpyrrolidone of the present application refers to a polymer obtained by polymerization of a vinylpyrrolidone monomer, and the modified compounds of the polyvinylpyrrolidone in the present application include polymers obtained by polymerization of a vinylpyrrolidone monomer and other monomers, such as olefins, alkynes, and alkylene oxides.

[0233] The polyvinylpyrrolidone and modified compounds thereof of the present application contain atoms such as nitrogen and oxygen, which are convenient for interacting with one or more of polar solvents such as alcohol solvents, acetone, and water, and at the same time, such atoms are also convenient for generating forces between metal ions of layered transition metal oxides, so that the layered transition metal oxide particles are dispersed in the solvent.

[0234] In some embodiments of the present application, the added amount of the above-mentioned dispersant is 0.5%-5% of the mass of the above-mentioned solvent.

[0235] In these embodiments, the present application discloses that the added amount of the above-mentioned dispersant is any one of 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5.0% of the mass of the above-mentioned solvent or satisfies any one of the above-mentioned range values.

[0236] In some embodiments of the present application, the above-mentioned solvent comprises one or more of alcohol solvents, acetone, and water.

[0237] The alcohol solvent includes one or more of ethanol, ethylene glycol, and glycerol. The solvent of the present application is mainly used for uniformly dispersing polyvinylpyrrolidone and modified compounds thereof.

[0238] In some embodiments of the present application, the solvent includes ethanol and water in a volume ratio of 1:1.

[0239] In some embodiments of the present application, after the intermediate product of the positive electrode material is dispersed in the mixed solvent and before the second calcination, the following step is further included:

[0240] The mixed solvent is heated to 70-100°C and stirred until the solvent is evaporated.

[0241] In some embodiments of the present application, the mass percentage of single crystal particles and single crystal-like particles in the positive electrode active material is 100%.

[0242] In some embodiments of the present application, the mass percentage of single crystal particles in the positive electrode active material is 20-40%, and the mass percentage of single crystal-like particles in the positive electrode active material is 60-80%.

[0243] In some embodiments of the present application, after the first calcination, the following steps are further included: rough breaking, fine crushing, and sieving to obtain the intermediate product of the positive electrode material, wherein the volume particle size distribution Dv50 of the intermediate product of the positive electrode material is 8-12 μm.

[0244] The determination method of the volume particle size distribution Dv50 of the intermediate product of the positive electrode material is as described above, and will not be repeated here. In these embodiments, the volume particle size distribution Dv50 of the intermediate product of the positive electrode material is any one of 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, and 12 μm, or satisfies any one of the above range values.

[0245] In some embodiments of the present application, the molar amount of metal atoms in the positive electrode material precursor is N1, the molar amount of sodium atoms in sodium carbonate is N2, and N1 / N2 satisfies 1:(0.5-1.1).

[0246] The positive electrode material precursor product in the present application and sodium carbonate undergo a solid-phase combination reaction through the first calcination. The material generated in the reaction mainly includes polycrystal particles formed by agglomeration. There are gaps between the single crystal grains of the polycrystal particles. After soaking in the solvent containing polyvinylpyrrolidone and modified compounds thereof, the force between the single crystal grains is weakened, and the single crystal grains or single crystal-like particles are decomposed during the second calcination.

[0247] Method for preparing a sodium secondary battery

[0248] The positive electrode sheet, the separator, and the negative electrode sheet are laminated in sequence, the separator is between the positive electrode sheet and the negative electrode sheet to play a separating role, a three-electrode copper wire is added, and the tabs are welded to form a laminated cell core; the laminated cell core is placed in an outer packaging shell, electrolyte is injected after drying, and the sodium secondary battery is obtained through processes such as vacuum packaging, standing, formation, and shaping.

[0249] The secondary battery of the present application will be described in detail below with specific examples.

[0250] The experimental methods used in the following examples are conventional methods unless otherwise specified.

[0251] The materials, reagents, etc. used in the following examples can be obtained commercially unless otherwise specified.

[0252] The present application can employ conventional techniques of inorganic chemistry within the skill of the art. In the following examples, efforts have been made to ensure accuracy with respect to numbers (amounts, temperature, reaction times, etc.) but some experimental errors and deviations should be accounted for. Temperatures used in the following examples are expressed in degrees Celsius, and pressures are at or near atmospheric pressure. All reagents are obtained at AR grade, and all reactions are carried out in an argon atmosphere. Unless otherwise indicated, all reagents are obtained from commercial sources.

[0253] Experimental materials:

[0254] 1. Polyvinylpyrrolidone: Aldrich (the decomposition temperature of polyvinylpyrrolidone is 450°C);

[0255] 2. Ethanol: Aldrich;

[0256] 3. Acetone: Aldrich.

[0257] Experimental apparatus:

[0258] 1. Box furnace: Kecheng OTF-1200X-S.

[0259] 2. Scanning electron microscope: Zeiss LEEQ0344.

[0260] Preparation Example 1-1

[0261] A method for preparing a layered oxide polycrystalline particle (chemical formula: NaNi 0.4 Fe 0.2 Mn 0.4 O2—NFM424) is provided:

[0262] S1, providing a precursor, including the following preparation process:

[0263] S11, according to the chemical formula Ni x1 Fey1 Mn z1 The metal element molar ratio in (OH)2is configured to prepare a metal salt mixed solution with a molar concentration of (2.0±0.4) mol / L, wherein 0≤x1≤1, 0≤y1≤1, 0≤z1≤1, x1+y1+z1=1, and a 30% mass fraction of sodium hydroxide solution, a 20% mass fraction of ammonia water and a 0.1% mass fraction of chelating agent solution (ethylenediaminetetraacetic acid) are configured; deionized water is added to the reaction kettle, and then the ammonia water, the chelating agent solution and the sodium hydroxide solution are sequentially added, the pH is controlled to be 10.8, and the reaction temperature is controlled to be 40℃-70℃±1℃;

[0264] S12, the metal salt solution, the sodium hydroxide solution, the ammonia water and the chelating agent solution are added to the reaction kettle, the flow rate ratio of the four solutions is 15:30:5:1, the nucleation is performed for 5h, then the sodium hydroxide flow rate is adjusted to reduce the pH to below 11.6 to complete the nucleation process; the metal salt solution, the sodium hydroxide solution, the ammonia water and the chelating agent solution are continuously added to the reaction kettle for co-precipitation reaction, the flow rate ratio of the four solutions is 15:30:5:1, the reaction pH is controlled to be 10.5, and the reaction is maintained for 48h to complete the growth process of the precursor particles;

[0265] S13, the solution in the above reaction kettle is transferred to a centrifuge for solid-liquid separation to obtain a positive electrode material precursor material containing water, and then the wet precursor material is dried at 120℃ for 20h to obtain a precursor finished product;

[0266] S2, preparing layered oxide polycrystalline particles: mixing the positive electrode material precursor with sodium carbonate, wherein the molar amount of metal atoms in the positive electrode material precursor is N1, and the molar amount of sodium atoms in the above sodium carbonate is N2, and N1 / N2 is 1:1.02;

[0267] The first calcination is performed in an oxygen-containing atmosphere (such as air or pure oxygen), the first calcination temperature is 850℃, the holding time is 13h, then the temperature is reduced to room temperature, and then rough breaking, fine crushing and screening are performed to obtain the layered oxide polycrystalline particles.

[0268] Test 1:

[0269] According to GB / T 19077-2016, the volume particle size distribution curve of the polycrystalline particles is obtained, and the particle size corresponding to the cumulative volume distribution percentage of 50% is taken as the average particle size Dv50, and the Dv50 of the polycrystalline particles of the preparation example 1-1 is 10.5μm.

[0270] Preparation example 1-1a

[0271] The layered oxide polycrystalline particles prepared in preparation example 1-1 are further processed, and the specific steps are as follows:

[0272] S3, providing a mixed solvent: 500 mL of ethanol and water were mixed in a volume ratio of 1:1 to form a solvent, and polyvinylpyrrolidone was added to the solvent to form a mixed solvent, and the mass of polyvinylpyrrolidone was 2% of the mass of the solvent;

[0273] dispersion: 10 g of the layered oxide polycrystalline particles prepared in Preparation Example 1-1 were dispersed in 30 mL of the above-mentioned mixed solvent, and the mixture was stirred and mixed to obtain a mixture;

[0274] heating: the mixture was transferred to a crucible, the mixed solvent was heated to 80°C, and the mixture was stirred under the condition of heat preservation until the solvent was completely evaporated, the stirring speed was controlled at 500 rpm, and after the solvent was evaporated, the remaining solid was obtained;

[0275] second calcination: the solid was transferred to a box furnace and calcined in air, the temperature of the box furnace was controlled at about 900°C, and the heat preservation time was 12 h;

[0276] warm down to room temperature: a layered oxide positive electrode active material was obtained.

[0277] Test 2:

[0278] (1) According to GB / T 19077-2016, the volume particle size distribution curve of the layered oxide positive electrode active material was obtained, and the particle size corresponding to the cumulative volume distribution percentage of 50% was taken as the average particle size Dv50. The Dv50 of the layered oxide positive electrode active material of Preparation Example 1-1a was 5.1 μm.

[0279] (2) According to GB / T 19587-2004, the nitrogen adsorption specific surface area analysis test method was used for testing, and the BET (Brunauer Emmett Teller) method was used for calculation to obtain the specific surface area BET of the layered oxide positive electrode active material. The specific surface area BET of the layered oxide positive electrode active material of Preparation Example 1-1a was 0.45 m 2 / g.

[0280] (3) According to GB / T5162-2006, the tap density of the layered oxide positive electrode active material was obtained, which was 1.68 g / cm 3 .

[0281] (4) According to the SEM spectrum in the above-mentioned characterization 2, the layered oxide positive electrode active material with a mass of m0 was separated to obtain layered oxide single crystal particles with a mass of m1 and layered oxide single crystal particles with a mass of m2.

[0282] According to the formula: (m1 ÷ m0) × 100%, the mass percentage content of the single crystal particles in the above-mentioned layered oxide positive electrode active material was calculated to be about 60%.

[0283] According to the formula: (m2 ÷ m0) x 100%, the mass percentage content of the quasi-single crystal particles in the above layered oxide positive electrode active material is about 40%.

[0284] Then, according to the above GB / T 19077-2016 standard, the particle size Dv50 of the single crystal particles and the quasi-single crystal particles is measured, and according to the above GB / T 19587-2004 standard, the specific surface area BET of the single crystal particles and the quasi-single crystal particles is measured. The specific is shown in Table 1 as follows.

[0285] Preparation Example 1-1b

[0286] The layered oxide polycrystalline particles prepared in Preparation Example 1-1 are further processed, and the difference between this processing method and Preparation Example 1-1a is that the mass of polyvinylpyrrolidone added is 5% of the mass of the solvent, and the temperature of the box furnace is controlled at about 995℃ during the second calcination, and the temperature is maintained for 10h. The others are the same as Preparation Example 1-1a.

[0287] According to the above test method of Preparation Example 1-1a, the following Table 1 data is obtained.

[0288] Preparation Example 1-1c

[0289] The layered oxide polycrystalline particles prepared in Preparation Example 1-1 are further processed, and the difference between this processing method and Preparation Example 1-1a is that the mass of polyvinylpyrrolidone added is 0.5% of the mass of the solvent, and the temperature of the box furnace is controlled at about 600℃ during the second calcination, and the temperature is maintained for 24h. The others are the same as Preparation Example 1-1a.

[0290] According to the above test method of Preparation Example 1-1a, the following Table 1 data is obtained.

[0291] Preparation Example 1-1d

[0292] The layered oxide polycrystalline particles prepared in Preparation Example 1-1 are further processed, and the difference between this processing method and Preparation Example 1-1a is that the solvent is prepared by mixing acetone and water in a volume ratio of 1:2 to form 500mL of solvent, and the temperature of the box furnace is controlled at about 610℃ during the second calcination, and the temperature is maintained for 10h. The others are the same as Preparation Example 1-1a.

[0293] According to the above test method of Preparation Example 1-1a, the following Table 1 data is obtained.

[0294] Preparation Example 1-1e

[0295] A preparation method of a layered oxide positive electrode active material is provided, and the preparation method comprises:

[0296] S1, providing a precursor, comprising the following preparation process:

[0297] S11, according to the chemical formula Ni x1 Fe y1 Mn z1 The molar ratio of metal elements in (OH)2is configured to prepare a mixed solution of metal salt with a molar concentration of (2.0±0.4) mol / L, wherein 0≤x1≤1, 0≤y1≤1, 0≤z1≤1, x1+y1+z1=1, and a 30% by mass sodium hydroxide solution, a 20% by mass ammonia solution, and a 0.1% by mass chelating agent solution (ethylenediaminetetraacetic acid) are also prepared; deionized water is added to a reaction kettle, followed by the addition of the ammonia solution, the chelating agent solution, and the sodium hydroxide solution, with the pH controlled at 10.8 and the reaction temperature controlled at 40-70°C±1°C;

[0298] S12, the metal salt solution, the sodium hydroxide solution, the ammonia solution, and the chelating agent solution are added to the reaction kettle, and the flow rate ratio of the four solutions is 15:30:5:1; after nucleation for 5h, the pH is reduced to below 11.6 by adjusting the flow rate of the sodium hydroxide solution to complete the nucleation process; the metal salt solution, the sodium hydroxide solution, the ammonia solution, and the chelating agent solution are continuously added to the reaction kettle for co-precipitation reaction, and the flow rate ratio of the four solutions is 15:30:5:1; the reaction pH is controlled at about 10.5, and the reaction is maintained for 48h to complete the growth process of the precursor particles;

[0299] S13, the solution in the above reaction kettle is transferred to a centrifuge for solid-liquid separation to obtain a wet positive electrode material precursor; the wet precursor material is dried at 120°C for 20h to obtain a precursor finished product;

[0300] S2, dispersion of the precursor finished product:

[0301] S21: providing a mixed solvent: 500mL of a mixed solvent is prepared by mixing ethanol and water in a volume ratio of 1:1, and polyvinylpyrrolidone is added to the solvent to form a mixed solvent, with the mass of the polyvinylpyrrolidone being 2% of the mass of the solvent;

[0302] S22: dispersion: 10g of the above precursor finished product is dispersed in 30mL of the above mixed solvent, and the mixture is stirred to obtain a mixture;

[0303] S23: heating: the mixture is transferred to a crucible, the mixed solvent is heated to 80°C, and stirring is performed under heat preservation until the solvent is completely evaporated; the stirring speed is controlled at 500rmp, and the remaining solid is obtained;

[0304] S3, calcination:

[0305] The remaining solid is mixed with sodium carbonate to obtain a mixture, wherein the molar amount of metal atoms in the remaining solid is N1, and the molar amount of sodium atoms in the sodium carbonate is N2, and N1 / N2 is 1:1.02; the mixture is calcined in an air atmosphere in a box furnace at a calcination temperature of 850°C for 13h, and then cooled to room temperature to obtain the layered oxide positive electrode active material.

[0306] Preparation Example 2-1

[0307] A layered oxide polycrystalline particle (chemical formula: NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2—NFM333)2is provided:

[0308] S1, providing a precursor, including the following preparation process:

[0309] S11, preparing a mixed solution of metal salts with a molar concentration of (2.0±0.4) mol / L according to the chemical formula Ni x1 Fe y1 Mn z1 x1+y1+z1=1, and a 30% by mass sodium hydroxide solution, a 20% by mass ammonia solution, and a 0.1% by mass chelating agent solution (ethylenediaminetetraacetic acid) are prepared; deionized water is added to a reaction kettle, and then the ammonia solution, the chelating agent solution, and the sodium hydroxide solution are sequentially added, and the pH is controlled to be 10.8, and the reaction temperature is controlled to be 40-70°C±1°C;

[0310] S12, adding the metal salt solution, the sodium hydroxide solution, the ammonia solution, and the chelating agent solution to the reaction kettle, and the flow rate ratio of the four solutions is 40:30:5:1, nucleation is performed for 5h, the pH is then reduced to below 11.6 by adjusting the flow rate of the sodium hydroxide solution to complete the nucleation process; the metal salt solution, the sodium hydroxide solution, the ammonia solution, and the chelating agent solution are continuously added to the reaction kettle to perform a coprecipitation reaction, and the flow rate ratio of the four solutions is 40:30:5:1, the pH of the reaction is controlled to be 10.8, and the reaction is maintained for 48h to complete the growth process of the precursor particles;

[0311] S13, transferring the solution in the reaction kettle to a centrifuge to perform solid-liquid separation to obtain a positive electrode material precursor material containing water, and then drying the wet precursor material at 120°C for 20h to obtain a precursor finished product;

[0312] S2, preparing a layered oxide polycrystalline particle: mixing the positive electrode material precursor with sodium carbonate, wherein the molar amount of metal atoms in the positive electrode material precursor is N1, and the molar amount of sodium atoms in the sodium carbonate is N2, and N1 / N2 is 1:1.05;

[0313] The layered oxide polycrystal particles prepared in Preparation Example 2-1 were further processed as follows:

[0314] Preparation Example 2-1a

[0315] The layered oxide polycrystal particles prepared in Preparation Example 2-1 were further processed as follows:

[0316] S3, providing a mixed solvent: 500 mL of a mixed solvent was prepared by mixing ethanol and water in a volume ratio of 1:1, and polyvinylpyrrolidone was added to the mixed solvent to form a mixed solvent, and the mass of the polyvinylpyrrolidone added was 2% of the mass of the solvent;

[0317] Dispersion: 20 g of the layered oxide polycrystal particles prepared in Preparation Example 2-1 were dispersed in 40 mL of the mixed solvent, and the mixture was stirred to obtain a mixed solution;

[0318] Heating: the mixture was transferred to a crucible, the mixed solvent was heated to 80°C, and the mixture was stirred under the condition of heat preservation until the solvent was completely evaporated, and a solid residue was obtained;

[0319] Second calcination: the solid residue was transferred to a box furnace, and calcination was performed in air, the temperature of the box furnace was controlled at about 700°C, and heat preservation was performed for 5 h;

[0320] Cooling to room temperature: a layered oxide positive electrode active material was obtained.

[0321] The following Table 1 data were obtained according to the test method of Preparation Example 1-1a.

[0322] Preparation Example 2-1b

[0323] The layered oxide polycrystal particles prepared in Preparation Example 2-1 were further processed as follows: the difference between this processing and Preparation Example 2-1a is that the mass of the polyvinylpyrrolidone added is 5% of the mass of the solvent, the temperature of the box furnace during the second calcination is controlled at about 985°C, and heat preservation is performed for 10 h. The others are the same as Preparation Example 2-1a.

[0324] The following Table 1 data were obtained according to the test method of Preparation Example 2-1a.

[0325] Preparation Example 2-1c

[0326] The layered oxide polycrystal particles prepared in Preparation Example 2-1 are further processed, and the difference between the processing method and Preparation Example 2-1a is that the mass of polyvinylpyrrolidone added is 0.5% of the mass of the solvent, the temperature of the box furnace is controlled at about 600°C during the second calcination, and the temperature is maintained for 24 hours. The other conditions are the same as those in Preparation Example 2-1a.

[0327] The following Table 1 data are obtained according to the test method of Preparation Example 2-1a.

[0328] Preparation Example 2-1d

[0329] The layered oxide polycrystal particles prepared in Preparation Example 2-1 are further processed, and the difference between the processing method and Preparation Example 2-1a is that the mass of polyvinylpyrrolidone added is 0.5% of the mass of the solvent, the temperature of the box furnace is controlled at about 600°C during the second calcination, and the temperature is maintained for 24 hours. The other conditions are the same as those in Preparation Example 2-1a.

[0330] The following Table 1 data are obtained according to the test method of Preparation Example 2-1a.

[0331] Preparation Example 2-1e

[0332] A preparation method of layered oxide positive electrode activity is provided, and the difference between the preparation method and Preparation Example 2-1a is that in step S3, polyvinylpyrrolidone is not added, and the other conditions are the same as those in Preparation Example 2-1a.

[0333] According to the above test method, and further test the particle size, specific surface area and tap density of the particles, the following Table 1 is obtained.

[0334] Preparation Example 3-1

[0335] A preparation method of layered oxide polycrystal particles (chemical formula: NaNi 0.4 Fe 0.2 Mn 0.3 Al 0.1 O2) is provided:

[0336] S1, providing a precursor, including the following preparation process:

[0337] S11, according to the chemical formula Ni x Fe y Mn z Al gA mixed solution of metal salts with a molar concentration of (2.0±0.4) mol / L is prepared, wherein the molar ratio of metal elements in (OH)2 is x: y: z: g, 0≤x≤1, 0≤y≤1, 0≤z≤1, 0≤g≤1; x+y+z+g=1; a 30% by mass sodium hydroxide solution, a 20% by mass ammonia solution, and a 0.1% by mass chelating agent solution (ethylenediaminetetraacetic acid) are also prepared; deionized water is added to a reaction kettle, followed by the addition of the ammonia solution, the chelating agent solution, and the sodium hydroxide solution, and the pH is controlled at 10.5, and the reaction temperature is controlled at 40-70℃±1℃;

[0338] S12, the metal salt solution, the sodium hydroxide solution, the ammonia solution, and the chelating agent solution are added to the reaction kettle, and the flow rate ratio of the four solutions is 50:30:5:1; nucleation is performed for 5h, then the pH is reduced to below 11.6 by adjusting the flow rate of the sodium hydroxide solution to complete the nucleation process; the metal salt solution, the sodium hydroxide solution, the ammonia solution, and the chelating agent solution are continuously added to the reaction kettle for co-precipitation, and the flow rate ratio of the four solutions is 50:30:5:1; the pH is controlled at 10.5, and the reaction is maintained for 48h to complete the growth process of the precursor particles;

[0339] S13, the solution in the reaction kettle is transferred to a centrifuge for solid-liquid separation to obtain a wet positive electrode material precursor; the wet precursor is dried at 120℃ for 20h to obtain a precursor product;

[0340] S2, layered oxide polycrystalline particles are prepared by mixing the positive electrode material precursor with sodium carbonate, wherein the molar amount of metal atoms in the positive electrode material precursor is N1, and the molar amount of sodium atoms in the sodium carbonate is N2, and N1 / N2 is 1:1.02;

[0341] The first calcination is performed in an oxygen-containing atmosphere (such as air or pure oxygen), the first calcination temperature is 950℃, and the holding time is 10h; then the temperature is lowered to room temperature; and the layered oxide polycrystalline particles are prepared by rough breaking, fine crushing, and sieving.

[0342] Preparation Example 3-1a

[0343] The layered oxide polycrystalline particles prepared in Preparation Example 3-1 are further processed, and the specific steps are as follows:

[0344] S3, a mixed solvent is prepared: 500mL of ethanol and water are mixed in a volume ratio of 1:1 to form a solvent, and polyvinylpyrrolidone is added to the solvent to form a mixed solvent, and the mass of the polyvinylpyrrolidone added is 2% of the mass of the solvent;

[0345] Dispersion: 20g of the layered oxide polycrystalline particles prepared in Preparation Example 3-1 are dispersed in 50mL of the mixed solvent to obtain a mixture;

[0346] Heating: The mixture was transferred into a crucible, the mixed solvent was heated to 80℃, and the mixture was stirred under the heating condition until the solvent was completely evaporated, and the remaining solid was obtained;

[0347] Second calcination: The solid was transferred into a box furnace, and calcination was performed in air, the temperature of the box furnace was controlled at about 700℃, and the temperature was maintained for 5h;

[0348] Warm down to room temperature: The layered oxide positive electrode active material was obtained.

[0349] The following Table 1 data was obtained according to the test method of Preparation Example 1-1a described above.

[0350] The scanning electron microscope (SEM) of the product of the preparation example was obtained:

[0351] Each sample was placed on a sample stage, placed in an electron microscope cabin, vacuumed, the electron beam was turned on, and appropriate parameters were set for characterization: the parameters for observing the morphology were 3kV, the aperture was 30μm, and the working distance was 5mm.

[0352] The precursor and the polycrystalline particles in Preparation Example 1-1 described above were subjected to the test method described above, and FIGS. 7A and 7B were obtained, wherein FIG. 7A is an SEM spectrum of the precursor, and FIG. 7B is an SEM spectrum of the polycrystalline particles; it can be seen from FIG. 7A that the precursor is uniform in size, and the particles are in a sheet shape; and it can be seen from FIG. 7B that the overall size of the particles does not change much after sodium supplementing and sintering, and the morphology is spherical.

[0353] The solid obtained by heating and the layered oxide positive electrode active material obtained by warm down to room temperature in Preparation Example 1-1a described above were subjected to the test method described above, and FIGS. 8A and 8B were obtained, wherein FIG. 8A is an SEM spectrum of the solid material obtained by heating, and FIG. 8B is an SEM spectrum of the layered oxide positive electrode active material obtained by warm down to room temperature; it can be seen from FIG. 8A that the addition of the dispersant is beneficial to the dispersion of the polycrystalline material; and it can be seen from FIG. 8B that after the second calcination, the particles are solid-solved, the particle size is large, and the morphology is good, mainly in a sheet shape.

[0354] The layered oxide positive electrode active material prepared in Preparation Example 1-1e described above was subjected to the test method described above, and FIG. 9 was obtained; it can be seen from FIG. 9 that the particles are agglomerated after the dispersion of the precursor, wherein the Dv50 of the primary particles is about 1.5μm, and the Dv50 of the agglomerated particles is about 8.5μm, which indicates that the dispersant has poor dispersion effect on the precursor.

[0355] The polycrystalline particles prepared in Preparation Example 2-1 described above were subjected to the test method described above, and FIG. 10 was obtained; it can be seen from FIG. 10 that the polycrystalline particles formed by agglomeration can be obviously observed, and the volume particle size distribution Dv50 of the particles is 10.8μm.

[0356] The layered oxide positive electrode active material obtained by heating the solid and cooling to room temperature was detected according to the above detection method, and FIGS. 11A and 11B were obtained, wherein FIG. 11A is an SEM image of the solid material obtained by heating, and FIG. 11B is an SEM image of the layered oxide positive electrode active material obtained by cooling to room temperature; as can be seen from FIG. 11A, the addition of the dispersant and the subsequent wet stirring affect the micro-morphology of the polycrystalline particles, the particles are broken and the surface morphology is changed, and as can be seen from FIG. 11B, the broken particles are solid-solutioned and become larger after high-temperature calcination.

[0357] The layered oxide positive electrode active material obtained by heating the solid and cooling to room temperature was detected according to the above detection method, and FIG. 11A is an SEM image of the solid material obtained by heating, and FIG. 11B is an SEM image of the layered oxide positive electrode active material obtained by cooling to room temperature; as can be seen from FIG. 11A, the addition of the dispersant and the subsequent wet stirring affect the micro-morphology of the polycrystalline particles, the particles are broken and the surface morphology is changed, and as can be seen from FIG. 11B, the broken particles are solid-solutioned and become larger after high-temperature calcination.

[0358] The particle size and other parameters of each preparation example are shown in Table 1.

[0359] Table 1

[0360] Example 1-1a

[0361] A sodium secondary battery is provided, which includes a positive electrode sheet, a separator film and a negative electrode sheet placed in sequence according to a stacking process, and further includes an electrolyte.

[0362] Preparation of a separator film:

[0363] A PE substrate with a thickness of 12 μm is provided.

[0364] Preparation of a negative electrode sheet:

[0365] Hard carbon, acetylene black and binder PAA are added to a blender in a weight ratio of 90:5:5, then deionized water is added, and the system is stirred under the action of a vacuum blender until it becomes uniform, obtaining a negative electrode slurry with a solid content of 60wt%. The negative electrode slurry is uniformly coated on both sides of the negative electrode current collector copper foil, wherein the coating width is 75mm and the coating area density is 11mg / cm 2 . A nine-section oven is used for drying, with the temperature settings being 100℃ / 100℃ / 95℃ / 85℃ / 85℃ / 80℃ / 80℃ / 80℃ / 60℃ in sequence, and then a cold press is used for compaction, so that the single-sided coating weight of the negative electrode film layer is 0.15g / 1540.25mm 2 .

[0366] Preparation of an electrolyte:

[0367] In an environment with a water content of less than 10ppm, non-aqueous organic solvents EC / EMC are mixed uniformly in a volume ratio of 3:7, then NaPF6 sodium salt (sodium salt concentration of 1mol / L) is added, and the mixture is uniformly mixed to obtain an electrolyte.

[0368] Preparation of positive electrode sheet:

[0369] The layered oxide positive electrode material prepared in Preparation Example 1-1a, acetylene black and PVDF were added to a blender in a ratio of 95:2.5:2.5, and then N-methyl pyrrolidone was added to form a positive electrode slurry with a solid content of 60%. The positive electrode slurry was coated on both surfaces of a positive electrode current collector aluminum foil, with a coating width of 70 mm and a positive electrode material coating area density of 19 mg / cm 2 , and dried by heating, specifically using a multi-section oven with temperature settings of 120°C / 100°C / 90°C in sequence, and then compacted using a cold press to obtain a positive electrode film layer with a compacted density of 3.0 g / cm 3 , and a single-sided coating weight of the positive electrode sheet of 0.34 g / 1540.25 mm 2 .

[0370] Preparation of sodium secondary battery:

[0371] The above positive electrode sheet, separator and negative electrode sheet were stacked in sequence, with the separator between the positive electrode sheet and the negative electrode sheet to serve as a separator, a three-electrode copper wire was added, and the tabs were welded to form a stacked cell. The stacked cell was placed in an outer packaging shell, dried, and then electrolyte was injected. After vacuum packaging, standing, formation, shaping and other processes, a sodium secondary battery was obtained.

[0372] Example 1-1b

[0373] A sodium secondary battery was provided, with the positive electrode active material being the layered oxide positive electrode active material prepared in Preparation Example 1-1b, and the other aspects being the same as Example 1-1a.

[0374] Example 1-1c

[0375] A sodium secondary battery was provided, with the positive electrode active material being the layered oxide positive electrode active material prepared in Preparation Example 1-1c, and the other aspects being the same as Example 1-1a.

[0376] Example 1-1d

[0377] A sodium secondary battery was provided, with the positive electrode active material being the layered oxide positive electrode active material prepared in Preparation Example 1-1d, and the other aspects being the same as Example 1-1a.

[0378] Comparative Example 1

[0379] A sodium secondary battery was provided, with the positive electrode active material being the layered oxide positive electrode active material prepared in Preparation Example 1-1e, and the other aspects being the same as Example 1-1a.

[0380] Example 2-1a

[0381] A sodium secondary battery was provided, the positive electrode active material of which was the layered oxide positive electrode active material of Preparation Example 2-1a, and the other components were the same as those of Example 1-1a.

[0382] Example 2-1b

[0383] A sodium secondary battery was provided, the positive electrode active material of which was the layered oxide positive electrode active material of Preparation Example 2-1b, and the other components were the same as those of Example 2-1a.

[0384] Example 2-1c

[0385] A sodium secondary battery was provided, the positive electrode active material of which was the layered oxide positive electrode active material of Preparation Example 2-1c, and the other components were the same as those of Example 2-1a.

[0386] Example 2-1d

[0387] A sodium secondary battery was provided, the positive electrode active material of which was the layered oxide positive electrode active material of Preparation Example 2-1d, and the other components were the same as those of Example 2-1a.

[0388] Comparative Example 2

[0389] A sodium secondary battery was provided, the positive electrode active material of which was the layered oxide positive electrode active material of Preparation Example 2-1e, and the other components were the same as those of Example 2-1a.

[0390] Example 3-1a

[0391] A sodium secondary battery was provided, the positive electrode active material of which was the layered oxide positive electrode active material of Preparation Example 3-1a, and the other components were the same as those of Example 1-1a.

[0392] [Performance Test]

[0393] The capacity retention rate of the test battery after 200 cycles at 25°C was tested:

[0394] 1C long cycle: 1C charge to 4.1V, constant voltage 0.05C→rest for 5min→1C discharge to 1.5V; for 1 cycle, record the discharge capacity at this time as Q1; after 200 cycles according to the above use conditions, record the discharge capacity as Q 200 , then the capacity retention rate is (Q1-Q 200 ) / Q1×100%.

[0395] Table 2

[0396] From the above examples, it can be seen that the design method provided by the application improves the content of single crystal particles and / or quasi-single crystal particles in the positive electrode material for sodium secondary batteries, thereby conveniently and better improving the cycle service life of the sodium secondary battery.

[0397] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the application, but not to limit them; although the application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the application, and they should be covered in the scope of the claims and the specification of the application. Especially, as long as there is no structural conflict, each technical feature mentioned in each embodiment can be combined in any way. The application is not limited to the specific embodiments disclosed in the text, but includes all technical solutions falling within the scope of the claims.

Claims

1. A sodium secondary battery characterized by: The positive electrode sheet, the separator, and the negative electrode sheet are stacked; The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer on at least one side surface of the positive electrode current collector; The positive electrode film layer comprises a positive electrode active material; The positive electrode active material comprises single crystal particles and / or quasi-single crystal particles of layered transition metal oxides; The shape of the single crystal particles and / or quasi-single crystal particles comprises any one or more of spherical, quasi-spherical, polygonal flaky, and polygonal columnar; And the positive electrode active material satisfies the following conditions: (1) the volume particle size distribution Dv50 is 3-7 μm; (2) a specific surface area BET of 0.3 m 2 / g ~ 0.5 m 2 / g.

2. The sodium secondary battery according to claim 1, characterized by: The mass percentage content of the single crystal particles in the positive electrode active material is 20-40%; And / or; The mass percentage content of the quasi-single crystal particles in the positive electrode active material is 60-80%.

3. The sodium secondary battery according to any one of claims 1 to 2, characterized by: The volume particle size distribution Dv50 of the single crystal particles is 5-7 μm; And / or; The volume particle size distribution Dv50 of the quasi-single crystal particles is 3-5 μm and does not include 5 μm.

4. The sodium secondary battery according to any one of claims 1 to 3, characterized by: The chemical formula of the layered transition metal oxide is Na x M y O z wherein M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, 0 < x < 1, 0 < y < 1, 1 < z < 2.

5. The sodium secondary battery according to any one of claims 1 to 4, characterized by: The layered transition metal oxide is a nickel iron manganese-based layered transition metal oxide having a chemical formula of NaNi a Fe b Mn c M1 d O2, wherein a+b+c+d = 1, 0 < a < 1, 0 < b < 1, 0 < c < 1, 0 < d < 1, and M1 is selected from one or more of Co, Cr, V, Al, Sn, B, Cu, Fe, Li, Ti, Mg, or Zn.

6. The sodium secondary battery according to any one of claims 1 to 5, characterized by: The compacted density of the positive electrode film layer is 3.0 g / cm 3 ~ 3.4 g / cm 3 .

7. The sodium secondary battery according to any one of claims 1 to 6, characterized by: The sodium secondary battery further comprises an electrolyte, and the electrolyte comprises any one or more of carboxylic acid ester compounds, carbonate compounds, and ether compounds.

8. A positive electrode active material for a sodium secondary battery, characterized by: The single crystal particles and / or quasi-single crystal particles comprise layered transition metal oxides; The shape of the single crystal particles and / or quasi-single crystal particles comprises any one or more of spherical, quasi-spherical, polygonal flaky, and polygonal columnar; The positive electrode active material satisfies the following conditions: (1) the volume particle size distribution Dv50 is 3-7 μm; (2) a specific surface area BET of 0.3 m 2 / g ~ 0.5 m 2 / g.

9. The positive electrode active material according to claim 8, characterized in that: The mass percentage content of the single crystal particles in the positive electrode active material is 20-40%; And / or; The mass percentage content of the quasi-single crystal particles in the positive electrode active material is 60-80%.

10. The positive electrode active material according to any one of claims 8 to 9, characterized by: The volume particle size distribution Dv50 of the single crystal particles is 5-7 μm; And / or; The volume particle size distribution Dv50 of the quasi-single crystal particles is 3-5 μm and does not include 5 μm.

11. The positive electrode active material according to any one of claims 8 to 10, characterized by: The tap density of the positive electrode active material is 1.55 g / cm 3 ~ 1.80 g / cm 3 .

12. A method for producing a positive electrode active material for a sodium secondary battery, characterized by: It comprises: A positive electrode material precursor is provided; A positive electrode material intermediate product is prepared: the positive electrode material precursor is mixed with sodium carbonate, and is subjected to first calcination to obtain the positive electrode material intermediate product, wherein the positive electrode material intermediate product comprises polycrystal particles of layered transition metal oxides; A positive electrode active material is prepared: a dispersant is dispersed into a solvent to form a mixed solvent, and the positive electrode material intermediate product is dispersed into the mixed solvent, and is subjected to second calcination to obtain the positive electrode active material, wherein the positive electrode active material comprises single crystal particles and / or quasi-single crystal particles of layered transition metal oxides, and the mass percentage content of the single crystal particles and quasi-single crystal particles in the positive electrode active material is greater than 98%; The dispersant satisfies the following conditions: (1) the dispersant is soluble in one or more of alcohol solvents, acetone, and water; (2) the decomposition temperature of the dispersant is less than or equal to 600 ℃, and the decomposition temperature of the dispersant is the temperature corresponding to the decomposition peak of the thermogravimetric curve of the dispersant.

13. The method of claim 12, wherein: The dispersant comprises polyvinylpyrrolidone and modified compounds thereof; And / or; The added mass of the dispersant is 0.5-5% of the mass of the solvent; And / or; The mass / volume ratio of the positive electrode material intermediate product to the mixed solvent is (10g-20g) / (20mL-100mL).

14. The method of any one of claims 12-13, wherein: The solvent comprises one or more of alcohol, acetone, and water. The alcohol comprises one or more of ethanol, ethylene glycol, and glycerol.

15. The method of any one of claims 12-14, wherein: The first calcination temperature is 850-970 DEG C, and the holding time is 7-15h; and / or; The second calcination temperature is 600-1000 DEG C, and the holding time is 3-24h; and / or; The first calcination and the second calcination are performed in an oxygen-containing atmosphere.

16. The method of any one of claims 12-15, wherein: After the positive electrode material intermediate product is dispersed in the mixed solvent, and before the second calcination, the method further comprises: The mixed solvent is heated and stirred until the solvent is evaporated.

17. The method of any one of claims 12-16, wherein: After the first calcination, the method further comprises rough breaking, fine crushing, and sieving to obtain the positive electrode material intermediate product, wherein the volume particle size distribution Dv50 of the positive electrode material intermediate product is 8-12um.

18. The method of any one of claims 12-17, wherein: The molar amount of metal atoms in the positive electrode material precursor is N1, and the molar amount of sodium atoms in the sodium carbonate is N2, and N1 / N2 is 1:(0.5-1.1).

19. An electrical device, comprising: The sodium secondary battery comprises the positive electrode active material of any one of claims 1-7 or the positive electrode active material prepared by the method of any one of claims 12-18. The sodium secondary battery comprises the positive electrode active material of any one of claims 1-7 or the positive electrode active material prepared by the method of any one of claims 12-18.

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